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Methimazole for Cats

Cat Hyperthyroidism Treatment

Methimazole is the generic form of Tapazole and is prescribed to cats to treat and control hyperthyroidism. Hyperthyroidism is a condition caused by excess thyroid hormones, and Methimazole regulates these hormones. The medication must be taken for life to ensure continued treatment.

Comparable Trade Names & Generics

Although methimazole is not approved by the FDA for use in veterinary medicine, it is commonly used by veterinarians for the treatment of hyperthyroidism in cats. Methimazole is not a cure for hyperthyroidism, but it is an effective treatment for the weight loss, rapid heart rate, vomiting, diarrhea, high blood pressure, increased appetite, increased urination, excessive thirst, and other symptoms of hyperthyroidism in cats. Methimazole can also help prevent complications of untreated hyperthyroidism.

Benefits of Methimazole:

  • Effectively manages hyperthyroidism and associated symptoms in cats
  • Results occur rapidly once treatment begins
  • Improves the quality of life of cats by preventing enlargement of the heart, heart failure, and damage to other organs
  • Safer than surgery
  • Lower incidence of side effects than propylthiouracil
  • Symptoms typically remain under control throughout life, provided treatment with methimazole continues

For Use In: This medication is not approved for veterinary use. However, this medication may be used to treat hyperthyroidism in cats.

Methimazole may also be used to protect the kidneys in dogs that are taking cisplatin, an anti-cancer drug. Speak with your veterinarian about using methimazole for this purpose.


  • Relieves symptoms of hyperthyroidism in cats to improve quality of life
  • Provides lasting control of hyperthyroidism when used continuously
  • Available in two strengths for convenient dosing

Product Details:

Methimazole is available in tablet form in two strengths: 5 mg and 10 mg.


Brand Name: Tapazole

Active ingredients: Methimazole

Inactive ingredients: Lactose Monohydrate, Povidone, Talc, Croscarmellose Sodium, Magnesium Stearate, Corn Starch.


Keep out of reach of children. Do not allow children to administer methimazole. Read directions and precautionary statements before use.

The usual dose of methimazole in cats ranges from 2.5 to 5 mg, two or three times per day.


  1. Give methimazole by mouth. If your cat refuses to accept the medication, use a pill pocket or hide the tablet in food to mask its bitter flavor.
  2. Administer 5 mg of methimazole by mouth every 8 to 12 hours, or as instructed by your doctor.
  3. See your veterinarian for blood testing every few weeks until the proper maintenance dose of this medication is obtained.
  4. Give a missed dose as soon as possible. If it is nearly time for the next dose, skip the mixed dose and resume a normal dosing schedule.

Frequency of Use:

Methimazole requires administration daily for the remainder of your cat's life.


Store out of reach of children and animals.

Store this product away from excess moisture and heat, at room temperature, and in its original packaging.

It is a violation of Federal Law to use this product in a manner inconsistent with its labeling.

Active ingredients: Methimazole

Inactive ingredients: Lactose Monohydrate, Povidone, Talc, Croscarmellose Sodium, Magnesium Stearate, Corn Starch.


Keep this product out of reach of children and animals. Do not use or store in or near open flame or heat.

CAUTION: Side effects of methimazole are typically more frequent and severe during the first 3 months of therapy. Common side effects include headache, joint pain, vomiting, loss of appetite, itching, rash, hives, drowsiness, and edema. Less common side effects include itching, yellowing of the skin or eyes, and other signs of liver problems. Consult your veterinarian immediately if these symptoms develop.

In some cases, treatment with methimazole may uncover kidney disease.

Rarely, use of this medication may cause myasthenia gravis, a neuromuscular condition that weakens muscles and causes swallowing problems. Call your doctor for an immediate appointment if your cat shows signs of bleeding or bruising or begins running a temperature over 103 degrees F.

Signs of allergic reaction include hives, scratching, sudden diarrhea, vomiting, pale gums, facial swelling, seizures, shock, cold limbs, or coma. These signs require emergency veterinary attention.

Do not administer methimazole to cats with autoimmune disease, blood abnormalities, or liver disease. Do not use this product in pregnant or nursing cats.

Methimazole may be contraindicated for use in cats that are taking warfarin, theophylline, beta-blockers, digoxin, propranolol, or metoprolol. Pets recently given a live vaccine should wait before starting methimazole. Pets should not be given a live vaccine while being treated with methimazole.

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Methimazole 10 mg, 100 Tablets
Availability: Rx Required
Retail: $32.99
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Methimazole 5 mg, 100 Tablets
Availability: Rx Required
Retail: $27.99
Price: $19.87
Item #: 1010038 -
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