Felimazole® (methimazole)

Active ingredient


Drug description:

This medication decreases the synthesis of thyroid hormones.


Methimazole is used to treat hyperthyroidism in cats.


Do not use, unless otherwise advised by a veterinarian, in cats with a carbimazole or polyethylene glycol allergy, immune mediated disease, diabetes mellitus, liver or kidney disease, bleeding disorder, or are pregnant or nursing.

For more information on this subject, talk to a veterinarian or consult the package insert that accompanies this product.

Side effects:  

The most common side effects are vomiting, decreased appetite, depression or decreased activity.

These effects typically occur during the first three months of therapy and are usually temporary.

Rarely, this medication can affect the production of white blood cells, red blood cells and platelets.

Even more rarely, this product can cause liver problems, itching of the face and the development of a neuromuscular disease called myasthenia gravis.

For more information on other possible side effects, please refer to the package insert that accompanies this product.

Recommended monitoring:

Make sure that the animal's condition improves and that he does not suffer from any side effects.

The animal should be re-evaluated periodically by the veterinarian to ensure the effectiveness of the therapy and the absence of damage to the internal organs and systems of the animal.

To do this, a physical examination and blood and urine tests should be performed regularly, at the beginning of treatment, every six months and during any change in dose.

Interactions with other drugs:

Methimazole can interact with benzimidazole, beta-blockers, bupropion, digoxin, phenobarbital, theophylline and warfarin.

It is important to notify the veterinarian if the animal is already receiving any of these medications when starting Felimazole ®.


At room temperature, in a dry place and protected from light. Excess heat or cold should be avoided.


Since this medication only controls hyperthyroidism but does not cure it, you should be aware that the therapy must be continued for the life of the animal.

It is best to wear gloves to handle the product and wash your hands afterwards. The tablets should not be cut or crushed.

Keep out of the reach of children and animals.

In the presence of severe, worsening or persistent side effects, contact a veterinarian as soon as possible.