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Pharmacotherapy of Thyroid Disorders

For medical students2 min readUpdated 2026-10-10

Pharmacological management of thyroid pathologies relies on two functionally opposing groups of medications. The choice of a specific drug depends on whether there is a need to replace a deficit of endogenous hormones or, conversely, to suppress their excessive production.

Replacement therapySynthetic analogs of natural hormones (T3 and T4) are used.
Target of thionamidesThyroid peroxidase enzyme involved in hormone synthesis.
Strumogenic effectEnlargement of the gland (goiter) during antithyroid drug therapy.
Role of TSHPituitary TSH hypersecretion stimulates thyroid tissue growth.

Classification of Drugs Affecting Thyroid Function

All pharmacological agents affecting thyroid functional activity can be divided into two main groups with directly opposing effects on the patient's body:

  1. Thyroid hormone medications — used as replacement therapy for hypofunction.
  2. Antithyroid agents (Thionamides/Thyrostatics) — used to suppress excessive hormone synthesis.

Replacement Therapy: Thyroid Hormones

This group of medications is designed to compensate for a deficiency of endogenous thyroid hormones. Synthetic analogs of natural compounds are used in clinical practice:

Antithyroid Agents (Thyrostatics)

Thyrostatics are prescribed for conditions accompanied by thyroid hyperfunction. The main representative of this group is Thiamazole.

Mechanism of Action: The action of thiamazole is based on the inhibition of a specific enzyme — thyroid peroxidase. Blockade of this enzyme disrupts the iodination of tyrosine residues within the thyroglobulin protein molecule. As a result of this cascade of reactions, the synthesis of the main thyroid hormones — T3 and T4 — is critically impaired and halted.

Adverse Effects: Strumogenic Action

The most characteristic and clinically significant adverse effect of thyrostatics (particularly thiamazole) is their strumogenic effect — the pathological enlargement of the thyroid gland leading to goiter formation.

Mechanism of the Strumogenic Effect: The development of goiter is explained by the physiological principle of negative feedback. During antithyroid drug therapy, there is a sharp decrease in circulating thyroid hormones (T3 and T4). The body responds to this deficit with pituitary hypersecretion of TSH (thyroid-stimulating hormone). Excess TSH exerts a powerful stimulatory effect on thyroid tissue, provoking its compensatory growth and hyperplasia.

Mnemonic

To remember the mechanism of thyrostatics: Thiamazole Throttles Thyroid peroxidase — T3 and T4 Tumble — TSH Triggers Tissue growth (goiter).

Frequently asked questions

What are the indications for levothyroxine administration other than replacement therapy for hypothyroidism?
  • Suppressive hormone therapy (levothyroxine sodium suppressive hormone therapy) — indicated in intermediate-risk, biochemical recurrence, and indeterminate tumor status groups in differentiated thyroid cancer to improve survival rates.
Which medications are used for thyroid hormone replacement therapy?

Levothyroxine (synthetic T4), liothyronine (synthetic T3), and their combinations are used for replacement therapy.

What is the mechanism of action of thiamazole?

Thiamazole inhibits the enzyme thyroid peroxidase, which blocks the iodination of thyroglobulin tyrosine residues and disrupts the synthesis of T3 and T4.

Why can a goiter develop during thyrostatic therapy?

Decreased levels of T3 and T4 trigger pituitary TSH hypersecretion via negative feedback. High TSH levels stimulate the proliferation of thyroid tissue (strumogenic effect).

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