Methimazole is a human drug that is used for the medical management of hyperthyroidism in cats. It currently is the drug of choice for the treatment of over-active thyroid and has largely replaced propylthiouracil for this purpose due to the lower incidence of side effects. Treatment with methimazole is a form of medical management; it does not cure the condition. Cats that are starting treatment should be monitored closely for the first three months. Blood counts and thyroid hormone levels should be measured every two to three weeks. Other blood tests for liver function and immune function may be performed as needed. The cat’s natural thyroid hormone levels will be reduced in one to three weeks. After your cat is stabilized on methimazole, blood tests for thyroid hormone levels usually are performed every three to six months.

Methimazole also is being used experimentally to protect the kidneys in dogs that are receiving cisplatin chemotherapy. If your veterinarian determines your pet has special needs that are not satisfied by the commercially available methimazole medication, he or she may prescribe compounded methimazole that is both the appropriate size and strength for your cat from a compounding pharmacy. In some instances a compounded transdermal preparation is prescribed. (What is compounding ?)


Methimazole treats hyperthyroidism in cats, a condition in which too much thyroid hormone is produced. It will not cure the disease, but will usually control it if given for the rest of the cat’s life. Methimazole may also be used to protect the kidneys in dogs receiving cisplatin, an anti-cancer drug.

  • – Controls the symptoms of hyperthyroidism for an improved quality of life
  • – Treats hyperthyroidism without surgery or anesthesia
  • – Affordable per-tablet price!

Methimazole (brand names: Tapazole®, Felimazole®) is an antithyroid medication used to treat hyperthyroidism in cats. Its use in cats and guinea pigs to treat hyperthyroidism is occasionally ‘off label’ or ‘extra label’. Many drugs are commonly prescribed for off label use in veterinary medicine. In these instances, follow your veterinarian’s directions and cautions very carefully as their directions may be significantly different from those on the label.

How is methimazole given

Methimazole is administered by mouth in the form of an oral tablet or is compounded as an oral liquid. It can also be applied to hairless skin (usually on the inside of the earflap) in the form of a transdermal gel. This medication can take days to weeks before effects are noted, and sometimes effects are not visibly obvious.

The oral form can be given with food or an empty stomach, but if your pet vomits or acts sick after receiving the medication without food, give it with food or a small treat. Follow all directions on the label, especially for compounded medications, and measure the liquid or gel doses carefully. This medication must be given for life, as it manages hyperthyroidism; it does not provide a cure. Pregnant and nursing women, or women who may become pregnant should wear gloves when handling the medication, cat litter, or body fluids from treated pets. Anyone applying the transdermal gel should wear gloves during administration.

Side Effects of Methimazole For Cats

Be sure to discuss any side effects with your veterinarian immediately. Adverse side effects usually occur within the first three months of therapy. The most common side effect is upset of the digestive tract. Up to 20% of cats may experience nausea, vomiting, loss of appetite and just not feel well. Usually this is self-limiting and most cats stop vomiting and begin to feel better without any change to the medication. A small number of cats will need to have their dose reduced. There is a lower incidence of digestive upset in cats that are receiving the transdermal gel, but it may take longer before the full effect of the transdermal treatment can be seen.

Within the first few weeks of treatment, a small number of cats self mutilate their face and neck through scratching. These animals will probably need to discontinue treatment. Temporary changes in blood counts are seen in about 15% of cats. These usually occur within the first two months of therapy. A very small number of cats will develop very serious changes in their bone marrow, blood counts or liver problems. Approximately 50% of animals receiving methimazole for more than six months develop other blood abnormalities (positive ANA). These cats may require a dose reduction. Very rarely, acquired myasthenia gravis (a disease that weakens muscles) may occur.


Methimazole is FDA-approved for the treatment of hyperthyroidism in cats. It may also be used to control hyperthyroidism in dogs with functional thyroid tumors (off-label use). Methimazole (Felimazole, is approved for use in the U.S. and other countries, while carbimazole (Vidalta, is approved for use outside the U.S.


Methimazole should not be used in cats with:

  1. Hypersensitivity to methimazole, carbimazole, or the excipient, polyethylene glycol
  2. Coagulopathies or hematologic disorders, such as anemia, neutropenia, lymphopenia, or thrombocytopenia
  3. Primary liver disease or renal failure (or use cautiously)
  4. Pre-existing autoimmune disease because autoimmune disorders (see Adverse Effects) have been reported in cats taking methimazole.

Methimazole should also not be used in pregnant or lactating queens; laboratory studies in rats and mice have shown evidence of teratogenic and embryotoxic effects of this medication.

Prices of Methimazole For Cats

$12.79 – $27.00

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