Thyrozol 20 mg film-coated tablets (thiamazole) – for treatment of an overactive thyroid (hyperthyroidism)

Thyrozol is a medicine containing thiamazole (methimazole), an active substance from the group of medicines used to treat thyroid disease (antithyroid agents). Thiamazole controls excessive production of thyroid hormones.

In Serbia the medicine is registered as 20 mg film-coated tablets with a score line on both sides, in a pack of 20 tablets. The dose is set individually according to the severity of the disease, thyroid function and iodine intake.

What is Thyrozol used for and how should it be taken?

Basic information about the medicine

What is Thyrozol used for?

According to the package leaflet, Thyrozol is used to treat excessive production of thyroid hormones (hyperthyroidism):

• as conservative treatment of an overactive thyroid, especially with a small goitre or without goitre;
• as preparation for thyroid surgery;
• as preparation for radioiodine treatment, especially in severe cases;
• after radioiodine treatment, until its effect has fully developed.

It is also used to prevent excessive hormone production before iodine exposure (e.g. examinations with iodine-containing contrast media) in people with mildly increased hormone production without other symptoms, with an autonomous adenoma or with a history of hyperthyroidism.

How is Thyrozol used and dosed?

The doctor sets the dose according to the severity of the disease. Usual doses according to the leaflet:

The 20 mg film-coated tablet can only be halved (10 mg); when doses of 2.5 mg or 5 mg are needed, this strength cannot be used. Swallow the tablet with enough liquid (e.g. half a glass of water) in the morning after breakfast; a higher daily dose can be divided into several doses at regular intervals.

Duration of treatment according to the leaflet: conservative treatment 6 months to 2 years; before surgery 3–4 weeks or longer; before radioiodine therapy until function normalises; after it about 4–6 months.

Special patient groups

• Children: the medicine must not be used in children aged 2 years and under; side effects in children and adolescents do not differ from those in adults.
• Liver or kidney impairment: tell your doctor – the dose will have to be reduced.
• Pregnant and breastfeeding women: see the pregnancy section – the lowest effective doses are used.

Contraindications – when the medicine must not be used

• hypersensitivity to thiamazole, other thionamide derivatives or the excipients;
• moderate to severe blood count disorder (granulocytopenia);
• bile stasis (cholestasis) present before the start of treatment;
• bone marrow damage after previous treatment with thiamazole or carbimazole;
• acute pancreatitis after previous use of thiamazole or carbimazole;
• use in combination with thyroid hormones during pregnancy.

Precautions and warnings

• If you have previously had mild allergic reactions to thiamazole (rash, itching), your doctor will decide whether you can take the medicine.
• With a large goitre that makes breathing difficult, the goitre may grow during treatment – the doctor may limit the duration of treatment with regular check-ups.
• Agranulocytosis: inflammation of the mouth, sore throat or fever – especially in the first weeks – require stopping the medicine and an urgent check-up.
• Fever or abdominal pain may be a sign of acute pancreatitis – inform your doctor immediately.
• At very high doses (more than 120 mg daily) the doctor periodically checks the blood count because of a possible effect on the bone marrow.
• Goitre growth or an underactive thyroid during treatment may require a dose review; endocrine orbitopathy may develop or worsen independently of the medicine.
• Weight gain is possible – a normal consequence of normalising the hormones that control energy use.
• The medicine contains lactose; it contains less than 1 mmol sodium per tablet.

Interactions with other medicines, food and drink

• Iodine: iodine deficiency increases and iodine excess decreases the thyroid response to thiamazole; the doctor sets the dose according to iodine intake.
• No direct interactions with other medicines are known. In an overactive thyroid other medicines are broken down faster, so as function normalises the doctor may adjust their doses.
• Anticoagulants (blood thinners): normalisation of thyroid function may affect their action – tell your doctor.

Pregnancy and breastfeeding

• Women who can become pregnant should use reliable contraception from the start of and during treatment.
• In pregnancy the medicine is taken only on the doctor's explicit recommendation after a benefit–risk assessment, at the lowest effective dose; additional thyroid hormone therapy must not be used during pregnancy.
• Thiamazole passes into breast milk: during breastfeeding it may be taken at the lowest possible doses (up to 10 mg daily), without additional thyroid hormones, with regular monitoring of the infant's thyroid function.

Driving and using machines

• Thyrozol has no influence on the ability to drive and use machines.

Possible side effects

Side effects may also occur several months after the start of treatment:

• Very common (more than 1 in 10): allergic skin reactions (rash, itching, hives), usually mild, which normally subside during treatment.
• Common (up to 1 in 10): joint pain.
• Uncommon (up to 1 in 100): agranulocytosis – fever, inflammation of the throat or mouth, sore throat.
• Rare (up to 1 in 1,000): taste disturbance; drug fever.
• Very rare (up to 1 in 10,000): decrease in platelets and other blood cells, enlarged lymph nodes, insulin autoimmune syndrome (marked drop in blood sugar), neuritis and polyneuropathy, swelling of salivary glands, cholestatic jaundice and toxic hepatitis, severe skin reactions (generalised dermatitis, Stevens-Johnson syndrome), hair loss, lupus.
• Not known: acute pancreatitis.

Overdose, missed dose and stopping treatment

• Overdose: no particular problems are expected after a single higher dose. If you have taken higher doses several times, contact your doctor immediately – the dose may need adjusting or thyroid hormones may be added to prevent goitre growth.
• Missed dose: do not take a double dose; continue on your usual schedule.
• Stopping treatment: your doctor decides on the duration and end of treatment.

Related information

During treatment, regular check-ups, monitoring of thyroid hormones and blood count as agreed with your doctor, and informing your doctor about all products containing iodine are important.

Composition, pack and manufacturer

• Active substance: thiamazole – 20 mg per film-coated tablet.
• Excipients – core: colloidal anhydrous silica; magnesium stearate; hypromellose 2910/15; powdered cellulose; talc; maize starch; lactose monohydrate; sodium starch glycolate; film coating: dimeticone 100, macrogol 400, titanium dioxide (E171), brown iron oxide (E172), hypromellose 2910/15.
• Appearance and pack: round, biconvex brown film-coated tablets with a score line on both sides; PVC/Al blister of 10 tablets, 2 blisters per carton (20 tablets).
• Marketing authorisation holder: Merck d.o.o. Beograd, Omladinskih brigada 90v, Belgrade. Manufacturer according to the ALIMS renewal list: P&G Health Austria GmbH & Co. OG, Austria. Authorisation 515-01-04554-18-001 of 05.02.2020.

Storage

• Store below 25 °C.
• Shelf life: 4 years; do not use after the expiry date on the carton and blister.
• Keep out of the sight and reach of children. Return unused medicine to a pharmacy that collects unused medicines.

Frequently asked questions

How long does treatment with Thyrozol last?

It depends on the reason for treatment. According to the leaflet, conservative treatment of hyperthyroidism usually lasts 6 months to 2 years, preparation for surgery 3–4 weeks or longer, and treatment after radioiodine about 4–6 months. Your doctor decides on the duration.

May I take vitamins or supplements containing iodine?

The amount of iodine affects the action of thiamazole – excess iodine reduces the thyroid response to the medicine. Therefore take iodine products (and seaweed) only with your doctor's agreement.

Can I divide the 20 mg tablet?

Yes, but only in half – giving a 10 mg dose. If you need a dose of 2.5 mg or 5 mg, the 20 mg tablets are not suitable.

Is it normal to gain weight during treatment?

The leaflet states that weight gain is possible and is a normal reaction of the body, because thiamazole normalises the thyroid hormones that control energy use.

Sources

• ALIMS – Patient information leaflet Thyrozol 20 mg (PIL)
• ALIMS – Summary of product characteristics Thyrozol 20 mg (SmPC)

Sources checked on: 25 October 2026.