Methimazole for Pets
Methimazole is an antithroid medication most commonly prescribed to treat hyperthyroidism in cats. It helps reduce excess thyroid hormone production and requires regular veterinary monitoring while your pet is taking it.
Methimazole Quick Facts
Drug class
Antithyroid medication
Common brand names
Felimazole®, Felanorm®; Tapazole® is a human brand name
Forms
Tablet and oral liquid; compounded forms may also be prescribed by a veterinarian
Species commonly prescribed for
Primarily cats; use in dogs is uncommon and should be directed by a veterinarian
What Methimazole Is Used For
Methimazole is used mainly to treat hyperthyroidism, especially in cats. It works by blocking the production of thyroid hormones, which can help control signs such as weight loss despite a good appetite, hyperactivity, vomiting, diarrhea, increased thirst, and a fast heart rate. In veterinary medicine, methimazole is often used for ongoing medical management, to stabilize a cat before surgery, or to help assess how a pet responds before considering other treatments such as radioactive iodine therapy. Dogs can also develop thyroid disease, but methimazole is not a routine long-term medication for most dogs and should only be used under direct veterinary guidance.
Side Effects to Watch For
Many pets tolerate methimazole well, but side effects are most likely to appear during the first few months of treatment. Watch for:
- Mild vomiting or nausea
- Decreased appetite
- Tiredness or lethargy
- Diarrhea
- Itching or scratching, especially around the face
- Skin redness or self-trauma from irritation
- More serious concerns such as jaundice, unusual bleeding or bruising, fever, severe weakness, or marked behavior changes
- Changes in kidney values or blood counts that may only be found on lab work, which is why regular monitoring is important
Dosing & Administration
Always follow your vet's instructions exactly. Do not change the dose, stop the medication, or switch formulations unless your veterinarian tells you to. Methimazole is usually given consistently on a schedule, and regular bloodwork is commonly needed to monitor thyroid levels, kidney function, and for possible adverse effects. If your pet spits out a dose, vomits after receiving it, or you are having trouble giving the medication, call your vet for guidance. Wash your hands after handling this medication, and ask your veterinarian for extra precautions if anyone in the household is pregnant, nursing, or immunocompromised.
When to Call a Vet
Go to the ER now
- ● Trouble breathing, facial swelling, collapse, or other signs of a severe allergic reaction
- ● Suspected overdose or accidental ingestion by another pet or a person
- ● Severe weakness, collapse, or seizures
- ● Persistent vomiting with inability to keep food or water down
See a vet within 24 hours
- ● Refusing food or marked drop in appetite
- ● Repeated vomiting or diarrhea
- ● Intense facial itching, scratching, or skin lesions
- ● Yellowing of the eyes, gums, or skin
- ● Unusual bruising, bleeding, fever, or profound lethargy
- ● New drinking or urination changes, or if your pet seems worse after starting treatment
Watch at home, call if it worsens
- ● Mild stomach upset shortly after starting the medication
- ● Temporary decrease in appetite that quickly resolves
- ● Mild tiredness while adjusting to treatment
Methimazole FAQs
Can I give my dog human methimazole?
What happens if I miss a dose?
Can my cat take methimazole?
Does my pet need blood tests while taking methimazole?
Can I stop methimazole if my pet seems better?
Disclaimer: The information provided in this article is for educational purposes only and does not constitute veterinary medical advice. Reading this content does not establish a veterinarian-client-patient relationship. Every pet is different — always consult a licensed veterinarian before making decisions about your pet's health, diet, or care. If you'd like personalized guidance, you can talk to one of our vets. If your pet is experiencing a medical emergency, contact your local emergency animal hospital immediately.