Is Methimazole (Tapazole) Safe for Cats?
Why it’s a problem
Methimazole is the most common treatment for feline hyperthyroidism, so many cat owners have it at home. The danger is misuse: human tablet strengths differ from veterinary products, and unsupervised dosing has been reported to cause vomiting, liver injury, and bone-marrow suppression. It must be dosed and monitored by a veterinarian.
How to keep your pet safe
Use only the veterinary prescription for your cat, follow the schedule exactly, and never adjust doses yourself. Keep household members’ own tablets stored separately so the pet supply is not confused.
Warning signs to watch for
Vomiting, diarrhea, drooling, loss of appetite, lethargy; overdosing over time: yellow gums or eyes, bruising, fever, weakness from blood-cell suppression.
When to call the vet
If your cat eats an unknown quantity, call your veterinarian or a pet poison hotline with the strength and number of tablets. Regular bloodwork is part of any veterinary methimazole treatment.
Common questions
My cat ate several of her methimazole tablets — is that bad?
Yes — an overdose can cause vomiting and, with larger amounts, liver or blood-cell injury. Call your vet or a pet poison hotline promptly with the tablet strength.
Can I buy methimazole myself and dose my hyperthyroid cat?
No. This drug needs veterinary diagnosis, prescription, and periodic bloodwork. Human formulations also differ from veterinary products, so self-dosing is unsafe.
More medications hazards for cats
This page is general educational information, not a substitute for professional veterinary advice. Every pet is different — if your animal ate or touched something concerning, contact your veterinarian or a pet poison hotline right away. In the US: Pet Poison Helpline (855) 764-7661, ASPCA Animal Poison Control (888) 426-4435 (fees may apply).