Hyperthyroidism Treatment for Pets

Tapazole is a safe, fast-acting treatment for hyperthyroidism. It does not cure the condition; it is used to manage related symptoms and prevent complications. Tapazole is taken for life when used to manage hyperthyroidism and is sometimes used before thyroid surgery or radioactive iodine treatment. Although it is not approved by the FDA for use in cats, such prescriptions are a common veterinary practice.

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Tapazole works rapidly to remedy hyperthyroidism in cats. It is better tolerated than propylthiouracil and rarely causes side effects, all of which are typically mild. Tapazole helps manage the rapid heart rate, coat problems, increased irritability, weight loss, excessive hunger and thirst, trouble with temperature regulation, diarrhea, vomiting, restlessness, hyperactivity, hypertension, weakness, and other symptoms associated with an overactive thyroid in cats.

Benefits of Tapazole:

  • Treats hyperthyroidism in cats
  • Lessens or eliminates the many symptoms associated with this condition
  • Helps prevent complications of hyperthyroidism
  • Improves the quality of life in animals with an overactive thyroid
  • Starts working quickly
  • Better tolerated than the alternative medication propylthiouracil
  • Does not usually cause side effects, and those that do occur are typically mild

Read the instructions and precautionary statements on the label prior to use.

Your veterinarian will need to perform blood tests every 3 to 4 weeks until an appropriate maintenance dose is established. Thereafter, your veterinarian will perform periodic blood tests (usually every 3 to 6 months).

The directions below represent a standard use. Follow the specifications of your veterinarian's prescription.


  1. Administer ½ to 1 tablet (2.5 to 5 mg) to cats 2 to 3 times per day.
  2. Give Tapazole with or without food.
  3. Allow access to plenty of fresh water with administration.

Frequency of Use:

Tapazole is generally given every 8 to 12 hours, or 2 to 3 times daily. It is taken for life.


Keep out of reach of children and animals.

Store Tapazole in its original container, tightly sealed, at room temperature. Protect from moisture and heat. Do not store in the bathroom. Use or discard by the expiration date.

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

Hyperthyroidism is a condition marked by excess thyroid hormone. Methimazole, the active ingredient in Tapazole, inhibits the production of thyroid hormone. This medication must be taken for life; if administration is discontinued, thyroid hormone levels will rise and symptoms of hyperthyroidism will return.

Tapazole Active Ingredients (per tablet): methimazole 5 mg

Tapazole Inactive Ingredients: Lactose Monohydrate, Magnesium Stearate, Starch (corn), Pregelatinized Starch, Talc


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

Tapazole is only intended for cats. Use only in the cat for which it was prescribed. Do not administer to other animals. Not for human use.

CAUTION: Do not administer in higher doses than prescribed. Use exactly as prescribed by your veterinarian.

Not for use in cats with a hypersensitivity to methimazole. Seek emergency veterinary treatment for an allergic reaction.

Do not give to cats with blood cell disorders, liver disease, or autoimmune diseases.

Not for pregnant or nursing animals.

Side effects may include diminished appetite, vomiting, drowsiness, edema, itching, hives, or rash. Mention any adverse reactions to your veterinarian.

Discontinue use and contact your veterinarian right away if your cat develops jaundice, fever, chills, easy bleeding or bruising, weakness, bloody stool or urine, or severe blistering or peeling.

Overdose may cause liver toxicity or blood disorders. Some symptoms include nausea, emesis, fever, and easy bruising. Seek emergency veterinary attention.

Tapazole increases the risk of bleeding and makes treated pets more susceptible to infections.

Do not administer a live vaccine to any cat taking Tapazole.

Tapazole can interact with other drugs and supplements. Check with your veterinarian before using any medications or supplements in your pet. Tell your veterinarian if your cat takes a beta-blocker, warfarin, digoxin, theophylline, metoprolol, propranolol, or other medications or supplements.

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