Thyroxine is one of two iodine-containing thyroid hormones. A deficiency or excess of production of the substance will cause disturbances in the body towards an unnatural slowdown or, on the contrary, acceleration of metabolism. Level correction is possible after diagnosis, under the supervision of an endocrinologist.

Thyroxine (T4) and triiodothyronine (T3) are thyroid hormones of the thyroid gland (iodothyronines). Iodothyronines, like other hormones, are bioactive substances that regulate the activity of the body. The bioactivity of T4 is low; in fact, it is the raw material for the production of T3.

Therefore, we should talk not so much about the functions of thyroxine, but about the role of thyroid hormones, expressed in the following aspects:

• increasing the rate of metabolic processes - the synthesis and breakdown of proteins, fats and carbohydrates, which allows you to release energy received from food and ensure optimal body weight and temperature;
• maintaining the activity of the brain (psyche and thinking) and endocrine glands (releasing insulin, pituitary and adrenal hormones). T4 and T3 promote stimulation of the nervous system and affect the duration of sleep;
• supplying body tissues with oxygen - by increasing the synthesis of transport proteins in the blood and stimulating respiration;
• support of heart function - blood flow, frequency and strength of contractions of the heart muscle, blood pressure, normalization of cholesterol levels;
• ensuring the tone of the muscular system - also applies to the smooth muscles of the internal organs (intestines);
• regulation of growth and development (in children and adolescents). In the first years of life, thyroid hormones influence the growth of the brain and skeleton;
• stimulation of reproductive function - the hormone causes thickening of the uterine mucosa in women in preparation of the body for conception. The normal level of thyroxine is necessary to maintain libido, normal potency in men and the course of menstruation in women.

Thyroxine does not have specific target organs that suffer from excess or deficiency. Violation of its concentration leads to system failures.

The effect of thyroxine can be ambiguous in case of serious deviations from the norm. For example, both reduced and excessive levels of the hormone can lead to impaired potency.

Thyroxine synthesis

The production of thyroxine occurs in the functional cells of the thyroid gland - thyrocytes.

The simplified synthesis algorithm is as follows:

1. Thyrocytes capture tyrosine (a protein from food) from the bloodstream, which is necessary for the production of thyroglobulin protein.
2. Capture and accumulation of iodine by thyrocytes.
3. Binding of thyroglobulin to iodine under the influence of the enzyme thyroid peroxidase.
4. Cleavage of the bound molecule to form 5–6 molecules of T4 and T3.

The breakdown of iodinated thyroglobulin and the release of hormones into the blood is regulated by the thyroid-stimulating hormone of the pituitary gland - TSH.

Differences between free and total thyroxine

When T4 is released into the bloodstream, most of it immediately binds to transport proteins. Only 0.1–0.4% remains unbound - this is free thyroxine.

The main differences between bound and free thyroxine are presented in the table:

Total thyroxine is the total concentration of bound and free hormone. Total thyroxine is easier to determine in the laboratory, but free thyroxine is a more informative indicator that allows you to immediately narrow down the range of possible disorders.

Differences between thyroxine and T3 hormone

Both thyroxine and T3 are iodinated derivatives of tyrosine. From the point of view of the structure of the molecule, the difference is in the number of iodine atoms - in thyroxine (T4) there are four, and in T3 there are three.

Thyroxine is a thyroid hormone with low biological activity. Most of T4 plays the role of a precursor to T3, into which it is converted in target organ tissues by removing 1 iodine atom. It is T3 that binds to cells and affects metabolism.

Hormones differ in the level of content in the bloodstream; the thyroid gland releases them in the following proportion:

• from 2/3 to 4/5 of thyroid hormones - in the form of thyroxine (T4);
• 1/3 or 1/5 – in the form of triiodothyronine (T3).

Hormone levels in men and women

Thyroxine is a thyroid hormone, the highest level of which is recorded in newborns. Closer to 20 years, it gradually falls and then remains unchanged.

Total thyroxine is measured in nmol/l, its norms are:

• 59–135 nmol/l (men);
• 71–142 nmol/l (women).

After 60 years, the norm does not depend on gender and is 65–138 nmol/l.

Free thyroxine is measured in pmol/l (since its level in the blood is much lower).

The rules are:

• 12.6–21 pmol/l (men);
• 10.8–22 pmol/l (women).

During pregnancy, total thyroxine is not informative; the norms of free hormone will differ by trimester:

• 1st trimester – 12.1–19.6;
• 2nd trimester – 9.6–17;
• 3rd trimester – 8.4–15.6.

Causes of thyroxine deficiency

Thyroxine is a thyroid hormone, the deficiency of which leads to the development of the hypothyroidism symptom complex.

Iodine deficiency (acute) leads to this condition infrequently, among the common causes:

• autoimmune thyroiditis – the immune system “attacks” the functional cells of the thyroid gland, destroying it;
• malignant degeneration of glandular tissue;
• congenital underdevelopment or absence of the gland;
• surgical treatment (removal of an organ - completely or most of it) or radioactive iodine therapy;
• disturbances in the functioning of the pituitary gland or hypothalamus (including postpartum necrotic process);
• suppression of the hormone already released into the blood due to blood poisoning, inflammation of the pancreas or shock conditions (sleep deficiency, stress);
• dietary features - lack of protein intake, selenium deficiency, excess potassium or calcium, which does not allow the gland to capture iodine;
• taking medications - narcotic substances, lithium, oral contraceptives, steroid hormones, Amiodarone, Analgin.

Hypothyroidism can result from conservative treatment of excess thyroxine in the blood (thyrotoxicosis).

Symptoms of deficiency

Hypothyroidism at an early stage may not manifest itself for 10-20 years (subclinical stage) - it can only be detected by a blood test for TSH.

The development of severe hypothyroidism gives many nonspecific (associated with other diseases) signs from:

• heart and blood vessels - slowing pulse, increasing lower pressure, increasing cholesterol levels in the blood with the appearance of atherosclerotic plaques;
• nervous system – lethargy, drowsiness, depression, impaired memory and concentration;
• digestive system – cholelithiasis, impaired motility of the biliary tract, constipation;
• musculoskeletal system – weakness and muscle cramps, swelling and pain in the joints;
• reproductive system - any menstruation disorders, infertility, erectile dysfunction;
• skin – hair loss, brittle nails, weight gain, dry skin and chilliness;
• excretory system - swelling, especially in the face, reduction of palpebral fissures, swelling of the nasal passages and tongue, causing difficulty speaking or nasal breathing.

The severity of symptoms can range from mild to life-threatening.

Causes of excess thyroxine

Excessive concentration of the hormone in most cases is caused by hyperfunction of the thyroid gland, which occurs against the background of:

During pregnancy, thyrotoxicosis can accompany severe toxicosis and hydatidiform mole (abnormal development of the embryo with the appearance of cysts).

Symptoms of excess

An increase in the concentration of T4 and T3 in the blood causes an inadequate acceleration of metabolic processes. The most dangerous sign of hyperthyroidism is the effect of hormones on the myocardium, causing palpitations, increased heart contractions, shortness of breath, arrhythmia, and swelling.

The reaction of other systems to hormonal stimulation is as follows:

• gastrointestinal tract - causeless diarrhea, enlarged liver, sudden weight loss with unchanged or even increased appetite. In old age, appetite may decrease;
• nervous system – nervousness, overexcitation, emotional instability, high speed of thought processes and speech, impaired concentration and sleep;
• reproductive system - scanty and irregular menstruation in women, decreased potency and gynecomastia (growth of mammary glands) in men, infertility;
• musculoskeletal system - decreased muscle mass, fatigue and tremors of muscles or limbs, destruction of bone tissue (osteoporosis);
• skin and hair – thinning of the skin and nails, hair loss, urticaria;
• thermoregulation – increased sweating, fever, intolerance to high temperatures;
• organs of vision - displacement of the eyeball forward and sometimes outward, with disturbance of its movement, rare blinking, double vision, dry eyes.

Thyroxine and pregnancy

Normally, the production of thyroxine during gestation increases - its production is stimulated by the “pregnancy hormone” HGT. An increase in T4 synthesis is required to provide energy to the mother’s body and build the child’s organs.

However, a non-physiological increase or lack of increase in thyroxine concentration can lead to negative consequences:

• structural anomalies of the internal organs and systems of the newborn;
• miscarriage;
• postpartum gland diseases in the mother and goiter in the fetus.

Hyper- and hypothyroidism during pregnancy are equally dangerous, but thyroxine deficiency is recorded much more often.

There are two main mechanisms for its appearance in women without previously identified disorders:

• work of the gland at the “limit” of its capabilities before conception causes asymptomatic hypothyroidism during pregnancy;
• the existing latent hypothyroidism becomes more pronounced during pregnancy.

Hypothyroidism is especially dangerous in the first trimester. Therefore, it is advisable to conduct a TSH test (a marker of reduced hormone production) before conception, and also necessarily at 8–12 weeks.

The study is mandatory for women at risk:

• those who have had thyroiditis;
• having confirmed gland dysfunction;
• suffering from autoimmune diseases or metabolic disorders.

If there is confirmed hypothyroidism in a woman planning a pregnancy, drug correction of hormonal levels is necessary before conception.

Analysis to determine the level of hormone concentration

To determine total/free T4, blood sampling from a vein is necessary.

It is produced:

• in the morning (most often) - dinner no later than 18.00;
• in the daytime - the interval after a light meal should be at least 4 hours (you can drink water);
• according to a specific schedule - if the analysis is carried out to monitor the prescribed therapy.

Knowing the date of the study, you must:

1. Stop taking steroid and thyroid hormones a month before.
2. For 3 days before the test, avoid alcohol, smoking (at least do not smoke for an hour before the test), avoid iodine intake, excess consumption of iodine-containing foods, spicy, fried foods and fast carbohydrates.
3. Minimize physical overload and stress during the day.
4. During the hour preceding the test, avoid excessive physical activity or nervousness.

In some cases, withdrawal of thyroid hormones is permissible for a shorter period - this should be discussed with an endocrinologist. You should also tell your doctor about any medications you are taking. To determine the concentration of thyroxine, blood serum is used, subjected to chemiluminescent immunoassay. The procedure takes several hours, and the result can be obtained the next day.

Decoding the analysis readings

A blood test for T4 cannot be the only test to diagnose hypo- or hyperthyroidism. The ratio of the hormones TSH, T3 and T4 (free) is important.

Basic patterns are presented in the table:

An endocrinologist is able to adequately assess the relationship between hormone levels (TSH, free and total T3 and T4) and prescribe further examination (ultrasound) or treatment.

Features of ultrasound testing for free thyroxine

Ultrasound examination of the thyroid gland reveals:

• an increase in volume (the norm is 19 ml for women and 25 ml for men), changes in the contours of the organ;
• diffuse (distributed) or nodular tissue changes;
• abscesses due to inflammation of the organ (thyroiditis);
• heterogeneous reduction in the size of the gland, areas of connective tissue in hypothyroidism.

The procedure is non-invasive and involves scanning the neck area with a sensor.

Among the features of preparation for ultrasound:

• no need to maintain an interval after eating. However, large meals should be avoided - to prevent the gag reflex when pressing the sensor on the neck;
• menstruation or pregnancy are not a contraindication to the procedure;
• During the ultrasound, you should relax your neck muscles and try not to move.

Treatment of hormone deficiency

Treatment tactics depend on the causes of the disease and individual characteristics (age, concomitant diseases).

The general patterns are:

• secondary hypothyroidism requires correction of the underlying disorder;
• drug-induced hypothyroidism is eliminated by stopping medications;
• Iodine deficiency hypothyroidism is treated by taking iodine and selenium, multivitamins.

However, replacement therapy is most often required - taking thyroxine (L-thyroxine).

The absolute indications for it are:

• severe hypothyroidism of any etiology;
• any type of deficiency in a pregnant woman or when planning to conceive;
• autoimmune thyroiditis (Hashimoto's disease);
• surgically removed thyroid gland or most of it.

In the last two cases, therapy is prescribed for life.

During treatment, the patient must follow a number of rules:

• The prescribed dose should be taken daily, without breaks;
• take a tablet once a day (regardless of the dose), in the morning, at least half an hour before meals (more is possible), with water;
• visit an endocrinologist on a prescribed schedule to monitor TSH - 3-4 measurements of the hormone level per year will allow you to determine the optimal dose, then the analysis is taken annually;
• regularly measure blood pressure and pulse; in case of failures, consult a doctor to adjust the dose (for patients with heart and vascular diseases).

The result after taking it is not noticeable immediately, sometimes it takes weeks to eliminate the symptoms.

Treatment of excess thyroxine

Hyperthyroidism is often combined with diffuse or nodular changes in the organ and tumors. Therefore, treatment tactics may include a surgical stage.

The conservative stage can be independent or precede radical treatment. It consists of taking thyreostatics - drugs that inhibit the production of hormones T3 and T4 - Thiamazole, Carbimazole, Propylthiouracil. Suppression of the “improper” functioning of the gland is combined with taking thyroid hormones in tablets - in order to avoid drug-induced hypothyroidism.

If there are single large nodes or growths of gland tissue - a section or an entire organ, as well as malignant degeneration, surgical removal of damaged tissue or an alternative option - radioactive iodine therapy is indicated.

The second method gives a result similar to the operation after 2-3 months, but does not allow the removal of large nodes or extensive diffuse changes.

For hyperthyroidism caused by an inflammatory process in the gland, it is permissible to use beta-blockers (Atenolol, Metaprolol, Propranolol) as a basic treatment, which do not reduce the release of hormones, but suppress their effect on the body.

Instructions for using drugs with thyroxine for weight loss

The use of thyroid hormones for weight loss has its pros and cons.

On the one hand, thyroxine promotes:

• acceleration of metabolic processes;
• burning calories and increasing performance during training;
• improving intestinal motility;
• decreased appetite – makes it easier to tolerate the diet.

On the other side:

• significant weight gain is rarely provoked only by hormonal imbalances - lifestyle also makes a contribution;
• Taking thyroxine in adequate doses should be combined with physical activity and proper nutrition. Significant weight loss only with taking the hormone requires large doses - such interference with hormonal levels is unsafe and can lead to the opposite result;
• from the point of view of endocrinologists, taking hormones without preliminary diagnosis is unacceptable;

Therefore, before use, it is advisable to take blood tests for TSH, T3, T4 and discuss the advisability of taking it with an endocrinologist. If hormones are produced in normal quantities, thyroid medications should be taken with extreme caution.

The general admission rules are:

• typical dose – 1.8 mcg per 1 kg of weight;
• dose for overweight – 2 mcg per 1 kg;
• dose for disorders of the heart and blood vessels – 0.9 mcg per 1 kg;
• you should start with a daily dose of 100 mcg (regardless of the plumb line), then it can be increased to 200–300 mcg.

Among the popular drugs with thyroxine:

The cost of one package with a dosage of 100 mcg per tablet for the listed drugs will be 120–180 rubles.

Homeopathy treatment

Thyroxine is a thyroid hormone, the concentration of which can be corrected using alternative medicine. The basis for homeopathic medicines is plant materials that are diluted to obtain small doses. Individually selected doses allow the use of the same drugs for hypo- and hyperfunction.

The basic principles of homeopathic treatment are:

• the raw materials for the drugs are minerals and other organic substances obtained from humans or animals;
• Treatment of advanced conditions allows for a combination of traditional and homeopathic remedies at the initial stage under the supervision of the attending physician and homeopath, then chemical medications are gradually discontinued.

Homeopathy is approved for use in children, pregnant women and the elderly.

It is optimal when the transition to homeopathic treatment is initiated by an experienced traditional medicine doctor.

When taking homeopathic remedies, you should follow a number of rules:

Popular drugs for hyperthyroidism are Scrofularia, Spongia, Iodum. Hypothyroidism is more difficult to eliminate with homeopathy; drugs are used - Thyroidin, Causticum, Spongia, Bromum, Selenium.

Increasing thyroxine levels at home

At home, to correct hypothyroidism, you can use photo remedies, folk recipes, and follow a special diet.

In this case, you should take into account:

• such treatment is acceptable for minor deviations from the norm without complications of deficiency, neoplasms or previous operations on the gland;
• one should not expect quick results from such therapy;
• home methods are more appropriate for prevention.

All home remedies are aimed at replenishing iodine deficiency; they cannot affect hypothyroidism caused by systemic diseases.

Traditional methods of treating thyroxine deficiency

Traditional medicine recipes are useful in combination; in the absence of contraindications and allergies, they can be used with virtually no restrictions.

Among the popular means:

Diet to normalize thyroxine levels

A slight decrease in thyroxine can be corrected by diet; in all other cases, following it will help the body in combination with medications.

The basic principles are:

• you should eat frequently (up to 6 times a day), in small portions;
• It is advisable to eat meals at the same time;
• consume less salt, strictly iodized;
• minimize the consumption of fatty, smoked, sweet and starchy foods, coffee, tea and alcohol;
• You need to drink clean water separately from food;
• increase the share of plant foods.

The composition of the menu is dictated by the need for iodine and proteins; you should consume more:

• seafood - seaweed and red fish;
• cucumbers, tomatoes, beets, radishes, spinach;
• apples;
• sources of protein - meat and legumes;
• milk and eggs.

For hyperthyroidism, the general rules are the same, but the diet should be higher in calories.

Should be excluded:

• pearl barley and barley porridge;
• baked goods and baked goods;
• fat meat;
• salty and spicy cheeses;
• cucumbers, radishes;
• tea, coffee, chocolate;
• rich meat, milk or bean soups.

Possible consequences and complications of improper or untimely treatment

Ignoring signs of hormone deficiency or attempting self-medication can cause:

The most dangerous complication of hyperthyroidism is thyrotoxic crisis (diagnosed only in women) - symptoms worsen to the point of heart failure, delirium, tissue degeneration of all organs, exhaustion and death. An excess of the hormone can lead to anorexia and osteoporosis.

Preventive measures

You can reduce the risk of hypo- and hyperthyroidism of various natures by taking into account the following recommendations:

• consume a sufficient amount of iodine with food or vitamins, but do not try to uncontrollably compensate for the noticed symptoms with it;
• maintain a sufficient level of protein in the diet, take multivitamins;
• establish a regime of work, rest and sleep;
• stop abusing alcohol and nicotine;
• if symptoms appear, contact an endocrinologist for diagnosis, and do not neglect preventive examinations;
• Avoid self-medication, independent dose changes, and discontinuation of medications containing thyroxine.

Thyroid hormones, including thyroxine, play a role in maintaining vital body functions. With adequate and timely treatment of hypo- and hyperthyroidism, the quality and life expectancy of patients does not suffer.

Article format: Lozinsky Oleg

Video about the hormone thyroxine

Thyroid hormones and their significance:

Thyroxine is a hormone that is produced and is necessary for its normal functioning and development. In addition, this hormone promotes the development of the body and its growth, and also increases the level and blood pressure. Let’s dot all the i’s right away - in the article we are discussing free thyroxine, that is, one that is in no way connected with transport proteins in the blood.

Thyroxine is a slimming hormone, because it is thanks to it that the overall metabolism in the body increases. One has only to think about why some thin girls can afford to eat in unlimited quantities and not gain weight at all. The correct answer is that their thyroxine levels in the blood are normal.

What determines the amount of thyroxine in the blood?

A normal level of this hormone in the blood will not only prevent you from gaining weight, but will also help tonify the entire body as a whole, as well as tonify brain processes.

The synthesis of thyroxine directly depends on the amount of iodine contained in our body. The relationship is simple - if the iodine content is normal, then the synthesis of the hormone will occur successfully; if the body does not receive enough iodine or somehow does not want to absorb it, then the synthesis of the hormone sharply decreases, and along with it, fat deposition increases.

Hypothyroidism - hormone deficiency

In addition, if the body is acutely lacking thyroxine, it becomes lethargic and inactive and cannot successfully solve the functional tasks assigned to it. The whole point is that the body redistributes the synthesized hormone to the needs of organs that support the vital functions of the body, in particular, for the needs of the heart and lungs, so there is simply not enough of this hormone for increased mental activity or intense sports.

People whose thyroxine hormone is greatly reduced? Quite often they experience fatigue and lethargy even after a long rest. Sports activities are abandoned due to the fact that it ceases to be interesting, and the exercises take too much energy - as a result, excess weight appears, which there is no desire to fight. Needless to say, it’s just a vicious circle. Also, the lack of this hormone affects the reproductive function of the body, reducing the ability of patients to become pregnant.

If you experience these symptoms, then first of all you should contact an endocrinologist and check the level of the hormone thyroxine T4 in the blood. If this is not just a passing apathy caused by emotional or life difficulties, then you should begin treatment. Treatment of hypothyroidism is not at all complicated and consists primarily of inflammation of the iodine reserves necessary for the body in any way - from a special diet to

Hyperthyroidism - increased hormone secretion

In addition, there is a downside to changing the normal content of this hormone in the body. So, if the thyroxine hormone is synthesized in smaller quantities, this can lead to rapid development. You should not rejoice in advance, because in the absence of proper treatment, the development of anorexia is more than real, and it can cause irreversible pathological processes in the body. In particular, you will be provided with early aging of the body and unpleasant wrinkles.

In order to reduce the level of iodine in the body, you first need to adhere to a strict diet, for example, you should completely exclude fish, milk, seaweed, eggs and mineral water from your diet.

Whatever one may say, the body needs thyroxine hormone in moderation. Any deviation from the norm will lead to negative consequences for you and your body, so if you have any symptoms, you must urgently get tested and consult with specialists, in this case you will save your body from unnecessary stress.

The thyroid gland is responsible for the speed of metabolic processes in the body, the tone of the cardiovascular and nervous systems. Biologically active substances in thyrocytes are formed using iodine molecules. The main thyroid hormones are thyroxine (T4) and triiodothyronine (T3).

Structure of thyroxine

Thyroxine is a derivative of the amino acid tyrosine. The hormone contains four iodine atoms. Iodine enters the thyroid gland with the blood. Compounds of this trace element are extremely important in the human diet. A lack of iodides in food and water can provoke endemic diseases (primarily diffuse and nodular goiter).

The molecular weight of thyroxine is 777 D. Approximately 83% of the weight is accounted for by iodine atoms. Chemical formula of T4: 3,5,3,5-tetraiodothyronine.

The synthesis of the hormone takes place in the follicles of the thyroid gland. The T4 hormone is formed as part of the thyroglobulin protein. First, two iodine atoms are added to tyrosine. Then two residues of the resulting diiodotyrosine molecules are combined. Alanine is split off from the compound.

The half-life of thyroxine is quite high and is 6–7 days.

Synthesis and secretion

Thyroxine is a weak thyroid hormone. The main activity of the thyroid gland is realized through triiodothyronine. This substance is formed from T4 in thyrocytes and in peripheral tissues (liver and others).

The conversion of thyroxine into its active form occurs with the help of the metalloenzyme selenium-dependent monodeiodase.

The thyroid gland produces and releases predominantly the hormone T4 into the blood. It normally accounts for 70–80% of the total amount of biologically active substances.

Thyroxine tends to accumulate in the thyroid tissue. It is then released into the blood as needed. The hormone is transported in bound form. Only a small portion circulates in free form.

Thyroxine transport proteins:

• transthyretin;
• serum albumin;
• thyroxine-binding globulin.

The hormone-globulin complex is the most stable compound.

Free forms of thyroxine are constantly found in the blood. Their concentration depends on tissue needs, thyrotropin levels and thyroid activity.

Free T4 can penetrate cell membranes and exert its biological effects.

The synthesis of thyroid hormones in the thyroid gland is subject to the regulatory influences of the pituitary gland and hypothalamus.

In the central links of the endocrine system there are:

• thyrotropin-releasing hormone of the hypothalamus;
• hypothalamic thyreostatin;
• pituitary thyrotropin.

Normally, the endocrine system interacts according to the feedback principle. The more thyroxine in the blood, the less stimulating factors (thyrotropin, thyrotropin-releasing hormone) are released. On the contrary, if the T4 hormone is synthesized in insufficient quantities, then the level of these substances increases.

Biological effect

Thyroxine does not have its own target cells. It affects all tissues. This substance is able to penetrate the membrane and connects with receptors in every cell of the body.

It is known that the affinity of thyroid receptors is higher for triiodothyronine. Therefore, only 10% of all thyroid effects are realized by T4.

Thyroxine hormone is considered a metabolic stimulator for many tissues. The hormone attaches to the cell nucleus and affects DNA-dependent RNA polymerase. As a result of this reaction, the intensity of protein synthesis increases.

A biologically active substance can also attach to cell mitochondria. These structures carry their own genetic information. Thyroxine stimulates oxidative phosphorylation in these structures.

The hormone stimulates energy consumption, increased oxygen consumption at the cellular level, increased protein and enzyme synthesis.

Effects of T4

The effect of the hormone on the body is diverse.

Main effects:

• participates in the growth and development of all organs and systems;
• increases metabolic rate;
• increases calorie consumption;
• increases the synthesis of thermal energy;
• increases tissue respiration;
• stimulates glycogen breakdown;
• inhibits glycogen formation;
• speeds up the heart rate;
• helps increase blood pressure;
• increases the tone of the nervous system;
• accelerates the formation of new blood cells;
• increases the reabsorption of water in the renal tubules;
• affects fat metabolism.

Normally, the balance of thyroxine and triiodothyronine contributes to the active functioning of a person. Both deficiency and excess of these substances lead to pathology.

Hormone norm

To accurately diagnose diseases, an endocrinologist often recommends tests for free forms of hormones. It is these indicators that characterize the state of the endocrine glands.

Normal free T4 values ​​depend on the gender and age of the patient.

In newborns, this indicator should be from 22 to 49 pmol/l. The norm for infants up to 10 weeks is from 9 to 21 pmol/l. At the age of 2.5 months to 5 years, the free T4 level in a child is normally 8–20 pmol/l. In older children, this hormone falls within the range of 8 to 17 pmol/l. In adults, free T4 is normal from 9 to 22 pmol/l. Women often experience higher thyroxine levels during pregnancy and when treated with estrogen.

Hypothyroidism and thyrotoxicosis

Lack of thyroxine – hypothyroidism. Its cause may be autoimmune thyroiditis, endemic goiter, surgery or radiation treatment. Patients with a deficiency of the hormone report weakness, drowsiness, memory impairment, dry skin, shortness of breath, and a rare pulse. Treatment of the disease is carried out by an endocrinologist. Patients are prescribed synthetic thyroxine.

Excess thyroid hormones lead to thyrotoxicosis. This condition accompanies diffuse toxic goiter, nodular goiter with autonomy, toxic thyroid adenoma. Patients' complaints are usually associated with rapid heartbeat, sweating, weight loss, trembling fingers, nervousness and insomnia. Treatment of thyrotoxicosis is carried out by specialists in clinics and hospitals. The drug effect is aimed at blocking the synthesis of thyroxine in the cells of the thyroid gland. For this purpose, thyreostatics are used.

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What is thyroxine? Thyroxine is a hormone produced by the thyroid gland. The substance is necessary to normalize the processes of oxidation and absorption of fats and carbohydrates in the body. Thus, it has a stimulating effect on metabolism.

It performs a large number of important functions in the human body. Therefore, it is important that its amount is always within the normal range. Deficiency and excess amounts of it in the blood can cause various diseases and dysfunctions of internal organs.

Main functions of the hormone

The substance is one of the few hormones that influence every cell of the human body. This is the reason for its high activity. Its main functions are:

• acceleration of metabolic processes - it has a stimulating effect on the synthesis of RNA and a number of other proteins that regulate metabolic processes in cells;
• activation of the thermoregulation center;
• ensuring the growth and functioning of each of the structures of the human body;
• the production of the substance increases the speed of the protein synthesis process;
• has an effect on vitamin metabolic processes;
• stimulating the work of the heart and blood vessels.

The substance also activates oxidation processes occurring in every cell of the body; under its influence they are accelerated.

Slender body

The thyroid gland plays an important role in human life. The substance it produces affects both the figure and the processes of the brain.

If this substance is produced in the amount necessary for a person, then problems with excess weight and any diseases of the central nervous system will not bother the person. But, if its production occurs in quantities exceeding the norm, health problems may arise:

• underweight (anorexia), even if the person does not adhere to any weight loss diet;
• rapid pulse, disturbances in the activity of the heart;
• insomnia or poor and restless sleep;
• lack of attention, a person cannot concentrate on some object or task (distracted attention is especially acute in drivers);
• the appearance of premature wrinkles in young women;
• brain activity decreases.

The amount of this substance in the blood depends on the amount of iodine in the human body. If iodine is not in deficient quantities in the human body, then the synthesis of all hormones (which are produced by the thyroid gland) will proceed successfully.

If the amount of iodine is much lower than normal, or for some reason it is not absorbed in the body, then the synthesis of other substances is reduced. In particular, a decrease in the level of the substance leads to active fat deposition and weight gain.

Substance deficiency

If thyroxine is produced in quantities much lower than normal, then the body’s activity decreases sharply. A person becomes sluggish; tasks that were previously solved in a short time now cause difficulty and a slow reaction.

Such changes occur because the brain needs to rationally distribute a substance that is produced in limited quantities. Therefore, first of all, it is necessary to provide them with organs and systems that are responsible for the vital functions of the body (lungs, brain, cardiovascular system).

Therefore, there is no longer enough thyroxine for active physical exercise and brain activity. Even pregnancy does not occur due to.

If signs of fatigue, lack of desire to engage in previously favorite and active sports, slow reactions, or lack of concentration appear, you should contact an endocrinologist.

If the cause is a lack of thyroxine, then it is necessary to undergo a course of treatment to restore vitality. The treatment is quite simple - increase the level of iodine in the body in various ways. You can use special diets and medications. And for severe iodine deficiency - injections.

Diagnosis of thyroxine deficiency

This substance has two fractions - bound and free. Modern laboratory tests detect free hormone in human blood. To detect thyroxine in the blood, it is necessary to take a blood test for , and TSH.

Depending on the quantity of these indicators in the human body, the endocrinologist can determine whether this is associated with any disease or not. However, laboratory tests alone are not enough for diagnosis.

The levels of thyroxine, the thyroid hormone, also depend on the time at which laboratory tests were carried out. It matters what equipment the tests were used on, as well as the research method used for this purpose. The normal value of thyroxine is in the range of 9–20 pmol/l. This applies to both male and female genders.

Treatment of thyroid diseases

For general human health, it is necessary to monitor whether the level of this substance is normal.

If it is much higher than the normal value, then the doctor prescribes a special therapeutic diet. What it is? The patient should exclude from the diet:

• seaweed;
• most species of sea fish;
• all dairy products;
• eggs.

But, if a therapeutic diet is carried out with the goal, on the contrary, of raising its level in the blood, then it is necessary to include all of the above products in your daily diet.

And also to increase its level, you should not eat foods that contain elements that interfere with the synthesis of the hormone in the thyroid gland. These products include:

• all citrus fruits;
• tomatoes;
• cucumbers

If there is a deficiency in the blood, the doctor may additionally prescribe its synthesized analogue, levothyroxine. In cases of severe thyroxine deficiency, this drug is taken regularly in small quantities, which promotes its synthesis in the thyroid gland.

Levothyroxine also has a stimulating effect on all cells of the body.

The importance of thyroxine balance in the human body

A normal level of this substance in human blood eliminates the risk of any diseases of the heart and blood vessels, and lipid metabolism in the blood also increases.

For a thyroid disease such as hypothyroidism, levothyroxine is prescribed to the patient for life to maintain all body functions. If the patient has only part of the thyroid gland during surgery, then this drug serves as replacement therapy.

This therapy allows you to maintain hormones, T3, in the body at the required level. Levothyroxine is prescribed even to children and women during pregnancy for certain indicators. But during the first and second semester, a pregnant woman must take a double dose, otherwise any pathologies may occur in the development of the child. You can take levothyroxine only as prescribed by your doctor.

One tablet of L-Thyroxine can contain from 25 to 200 mcg levothyroxine sodium .

The composition of excipients may vary slightly depending on which pharmaceutical company produced the drug.

Release form

The product is available in tablet form and is supplied to pharmacies in packages No. 25, No. 50 or No. 100.

pharmachologic effect

L-Thyroxine is thyroid stimulant , which is used when hypofunction of the thyroid gland (TG) .

Pharmacodynamics and pharmacokinetics

Levothyroxine sodium , which is part of the tablets, performs the same functions as endogenous ones (produced by the human thyroid gland) And . In the body the substance is biotransformed to liothyronine , which, in turn, penetrating into cells and tissues, affects the mechanisms of development and growth, as well as the course of metabolic processes .

In particular, L-Thyroxine is characterized by the ability to influence the oxidative metabolism occurring in mitochondria and selectively regulate the flow of cations both in the intracellular space and outside the cell.

The effect of a substance depends on its dosage: the use of the drug in small doses provokes an anabolic effect, in higher doses it affects mainly cells and tissues, increasing the latter’s need for oxygen, stimulating oxidative reactions, accelerating the breakdown and metabolism of fats, proteins and carbohydrates , activating functions hearts , vascular system And CNS .

Clinical manifestation of action levothyroxine at observed already in the first 5 days after the start of treatment. Over the next 3-6 months, subject to continuous use of the drug, it decreases or completely disappears.

Levothyroxine taken orally is absorbed primarily in the small intestinal tract. Absorption is largely determined by the galenic form of the drug - max up to 80% when taken on an empty stomach.

The substance binds to plasma proteins almost 100%. This is due to the fact that levothyroxine does not respond to any hemoperfusion , neither hemodialysis . Its half-life is determined by the concentration of thyroid hormones in the patient’s blood: when euthyroid states its duration is 6-7 days, with thyrotoxicosis - 3-4 days, for hypothyroidism - 9-10 days).

About a third of the administered substance accumulates in liver . At the same time, it quickly begins to interact with levothyroxine, which is in.

Levothyroxine is broken down primarily in muscle tissue , liver And brain tissue . Active liothyronine , which is a product of the metabolism of the substance, is excreted in the urine and intestinal contents.

Indications for use

L-Thyroxine is used for maintenance HRT when hypothyroid conditions of various origins , including including primary and secondary hypothyroidism developed after surgery on the thyroid gland, as well as conditions provoked by therapy using radioactive iodine preparations .

It is also considered appropriate to prescribe the drug:

• at hypothyroidism (both congenital and in the case where the pathology is a consequence of lesions hypothalamic-pituitary system );
• for obesity and/or cretinism , which are accompanied by manifestations hypothyroidism ;
• at cerebral-pituitary diseases ;
• as a prophylactic for recurrent nodular goiter after resection of the thyroid gland (if its function is not changed);
• for treatment diffuse euthyroid goiter (L-Thyroxine is used as an independent remedy);
• for treatment euthyroid hyperplasia of the thyroid gland , and Graves' disease after compensation for intoxication has been achieved thyroid hormones with help thyreostatic drugs (as part of complex therapy);
• at Graves' disease And Hashimoto's disease (in complex treatment);
• for the treatment of patients with hormone-dependent well-differentiated malignant neoplasms in the thyroid gland (including papillary or follicular carcinoma );
• for suppressive therapy and HRT in patients with malignant neoplasms in the thyroid gland (including after surgery for thyroid cancer ); as a diagnostic tool when conducting tests thyroid suppression .

In addition, thyroxine is often used in bodybuilding as a means of losing weight.

Contraindications

L-Thyroxine is contraindicated for use in:

• hypersensitivity to the drug;
• acute;
• acute inflammatory lesions of the heart muscle ;
• untreated thyrotoxicosis ;
• untreated hypocortisolism ;
• hereditary galactosemia , lactase deficiency , malabsorption syndrome .

The drug should be used with caution in patients with diseases of the heart and blood vessels (including including , myocardial infarction in the anamnesis, arterial hypertension ), long-term severe form hypothyroidism , .

The presence of any of the above diseases in the patient is a prerequisite for changing the dose.

Side effects of L-Thyroxine

Correct use of the drug under the supervision of a physician is not accompanied by side effects. In hypersensitive individuals, treatment with levothyroxine may be accompanied by allergic reactions .

Other side effects are usually caused by an overdose of L-Thyroxine. Extremely rarely, they can be triggered by taking the medicine in an incorrectly selected dose, as well as by increasing the dose too quickly (especially in the initial stages of treatment).

Side effects of L-Thyroxine are most often expressed as:

• feelings worries , headaches , insomnia , pseudotumor cerebri;
• arrhythmias (including atrial fibrillation), tachycardia , angina pectoris , heartbeat , extrasystoles ;
• vomiting and;
• skin rashes, skin itching , ;
• pathologies of the menstrual cycle ;
• , hyperthermia, feeling hot, weight loss, increased weakness, muscle cramps .

The appearance of the above symptoms is a reason to reduce the dose of L-Thyroxine or stop treatment with the drug for several days.

Cases of sudden death have been recorded due to cardiac disorders in patients using levothyroxine in high doses for a long time.

After the disappearance of side effects, therapy is continued, carefully selecting the optimal dose. Whenever allergic reactions (bronchospasm , laryngeal edema and - in some cases -) the use of the drug is stopped.

L-Thyroxine: instructions for use

The daily dose of the drug is determined individually depending on the indications. The tablets are taken on an empty stomach with a small amount of liquid (without chewing), at least half an hour before meals.

Patients under 55 years of age with healthy heart and blood vessels during replacement therapy are advised to take the drug at a dose of 1.6 to 1.8 mcg/kg. Persons who have been diagnosed with certain heart/vascular diseases , as well as for patients over 55 years of age, the dose is reduced to 0.9 mcg/kg.

For persons whose body mass index exceeds 30 kg/sq.m, the calculation is made based on “ ideal weight”.

At the initial stages of treatment hypothyroidism The dosage regimen for different patient groups is as follows:

• 75-100 mcg/day/100-150 mcg/day. - respectively, for women and men, provided that their heart and vascular system are functioning normally.
• 25 mcg/day. - persons over 55 years of age, as well as persons diagnosed with cardiovascular diseases. After two months, the dose is increased to 50 mcg. The dose should be adjusted by increasing it by 25 mcg every next 2 months until the indicators normalize thyrotropin in blood. If cardiac or vascular symptoms occur or worsen, a change in treatment regimen is required. heart/vascular diseases .

In accordance with the instructions for use of levothyroxine sodium, patients with congenital hypothyroidism the dose should be calculated depending on age.

For children from birth to six months, the daily dose varies from 25 to 50 mcg, which corresponds to 10-15 mcg/kg/day. when converted to body weight. Children from six months to one year are prescribed 50-75 mcg/day, children from one to five years old - from 75 to 100 mcg/day, children over 6 years old - from 100 to 150 mcg/day, adolescents over 12 years old - from 100 to 200 mcg/day.

The instructions for L-Thyroxine indicate that infants and children under 36 months of age should be given the daily dose in one dose, half an hour before the first feeding. Immediately before administration, the L-Thyroxine tablet is placed in water and dissolved until a thin suspension is formed.

At hypothyroidism El-Thyroxine is usually taken throughout life. At thyrotoxicosis after it is reached euthyroid state , levothyroxine sodium is prescribed to be taken in combination with antithyroid drugs . The duration of treatment is determined by the doctor in each specific case.

Regimen for taking L-Thyroxine for weight loss

In order to lose extra pounds, the drug should be taken at a dose of 50 mcg/day, dividing the indicated dose into 2 doses (both doses should be taken in the first half of the day).

Therapy is supplemented with the use β-blockers, the dose of which is adjusted depending on the pulse rate.

Subsequently, the dose of levothyroxine is gradually increased to 150-300 mcg/day, dividing it into 3 doses until 18:00. At the same time, the daily dose is increased β-blocker . It is recommended to select it individually, so that the resting heart rate does not exceed 70 beats per minute, but at the same time is greater than 60 beats per minute.

The appearance of pronounced side effects is a prerequisite for reducing the dose of the drug.

The duration of the course is from 4 to 7 weeks. The medication should be stopped gradually, reducing the dose every 14 days until complete discontinuation.

If during use there is diarrhea , the course is supplemented with a prescription, which is taken 1 or 2 capsules per day.

Between courses of taking levothyroxine, intervals of at least 3-4 weeks should be maintained.

Overdose

Symptoms of overdose are:

• increased heart rate and pulse;
• increased anxiety;
• feeling of heat;
• hyperthermia ;
• hyperhidrosis (excessive sweating);
• insomnia;
• arrhythmia ;
• increased frequency of attacks angina pectoris ;
• weight loss;
• anxiety;
• tremor ;
• diarrhea ;
• vomit;
• muscle weakness and convulsions ;
• pseudotumor cerebri;
• menstrual cycle irregularities .

Treatment involves stopping taking L-Thyroxine and conducting follow-up examinations.

With the development of severe tachycardia to reduce its severity, the patient is prescribed β - adrenergic blockers . Due to the fact that the thyroid function is completely suppressed, use thyreostatic drugs not advisable.

When taking levothyroxine in extreme doses (during a suicide attempt), it is effective to plasmapheresis .

Interaction

The use of levothyroxine reduces the effectiveness antidiabetic drugs . At the beginning of treatment with the drug, as well as each time the dose is changed, monitoring should be carried out more frequently. blood glucose level .

Levothyroxine potentiates effects anticoagulants (in particular, the coumarin series), thereby increasing risk of cerebral hemorrhages (dorsal or head), as well as gastrointestinal intestinal bleeding (especially in older people).

Therefore, if it is necessary to take these drugs in combination, it is recommended to carry out regular blood clotting tests and, if appropriate, reduce the dose anticoagulants.

The action of levothyroxine may be impaired when taken concomitantly with protease inhibitors. In this regard, it is necessary to constantly monitor the concentration of thyroid hormones. In some situations, it may be necessary to review the dose of L-Thyroxine.

Cholestyramine And colestipol slow down the absorption of levothyroxine, so L-Thyroxine must be taken at least 4-5 hours before taking these medications.

Drugs containing aluminum or iron may reduce the severity of the effects of levothyroxine, so take L-Thyroxine at least 2 hours before taking them.

The absorption of levothyroxine is reduced when taken in combination with lanthanum carbonate or sevelamer , therefore, it should be taken one hour before or three hours after using these remedies.

When taking drugs in combination, monitoring the level of thyroid hormones is necessary at the initial and final stages of their simultaneous use. The dose of levothyroxine may need to be adjusted.

The effectiveness of the drug decreases when taken simultaneously with tyrosine kinase inhibitors, therefore, changes in thyroid function should be kept under control during the initial and final stages of simultaneous use of these drugs.

Proguanil/chloroquine And reduce the effectiveness of the drug and provoke an increase plasma concentration of thyrotropin .

Drug-induced enzymes (eg. carbamazepine or barbiturates ) may increase the concentration of levothyroxine.

Women taking hormonal contraceptives , which contains estrogenic component , as well as for women taking postmenopausal age hormone replacement drugs , the dose of levothyroxine may need to be increased.

Thyroxine and L-Thyroxine

Which is better: Eutirox or L-Thyroxine?

The drugs are generics, that is, they have the same indications for use, the same range of contraindications and are dosed similarly.

Difference Euthyroxa and L-Thyroxine is that it contains Euthyroxa Levothyroxine sodium is present in slightly different concentrations than in L-Thyroxine.

Combination with alcohol

A single dose of a small dose of alcohol that is not too strong, as a rule, does not provoke any negative consequences for the body, so the instructions for the drug do not categorically prohibit such a combination.

However, it is permissible only for patients with healthy heart and blood vessels.

Drinking alcohol during treatment with L-Thyroxine often provokes a number of undesirable reactions from the central nervous system and liver, which in turn can affect the effectiveness of treatment.

L-Thyroxine for weight loss

According to its effectiveness thyroxine significantly superior to most fat burning products (including pharmacological ones). According to the instructions, it speeds up , increases calorie expenditure, enhances heat production, stimulates the central nervous system, suppresses appetite, reduces the need for sleep and increases physical performance.

In this regard, there are many positive reviews about the use of levothyroxine sodium for weight loss. However, those who want to lose excess weight should remember that the drug increases heart muscle contraction frequency , causes a feeling of anxiety and excitement, thereby having a negative effect on the heart.

To prevent the development of side effects, experienced bodybuilders advise using el-thyroxine for weight loss in combination with antagonists (blockers) β-adrenergic receptors . This allows you to normalize your heart rate and reduce the severity of some other side effects that accompany taking thyroxine.

The advantages of L-Thyroxine for weight loss are the high efficiency and availability of this drug, the disadvantage is a large number of side effects. Despite the fact that many of them can be eliminated or even prevented, it is recommended to consult a specialist before using the drug in order to lose extra pounds.

Use during pregnancy

Treatment with thyroid hormones should be carried out consistently, especially during pregnancy and lactation. Despite the fact that L-Thyroxine is used quite widely during pregnancy, there is no exact data on its safety for the developing fetus.

The amount of thyroid hormones penetrating into breast milk (even if therapy is carried out using high doses of the drug) is insufficient to provoke in an infant inhibition of thyrotropin secretion or development thyrotoxicosis .