Medication Guide • Reviewed by Dr. Tiffany Delacruz, DVM
Methimazole (Felimazole, Tapazole) for Cats
Methimazole is the most common prescription treatment for hyperthyroidism in cats — a condition affecting roughly 10% of senior cats.
What Methimazole (Felimazole, Tapazole) is used for in cats
- Hyperthyroidism in cats
- Pre-radioactive-iodine treatment workup
How it works
Methimazole blocks thyroid hormone production in the thyroid gland, lowering circulating T4 levels back toward normal.
Available formulations
2.5 mg tablet
5 mg tablet (Felimazole)
Transdermal gel (compounded)
Compounded liquid
Side effects to know
Common side effects
- • Vomiting
- • Decreased appetite
- • Lethargy (first 1-4 weeks)
These usually resolve on their own. If they persist past the first few doses, ask your vet.
Call your vet immediately if you see
- ⚠ Bone marrow suppression (rare)
- ⚠ Liver toxicity (rare)
- ⚠ Facial itching/scratching (allergic)
Drug interactions
- • Other immune-affecting drugs
When not to use
- • Cats with bone marrow disease
- • Documented hypersensitivity
Monitoring during treatment
Bloodwork at 2-3 weeks after starting, then 1-2 months, then every 3-6 months long-term. T4 level guides dose adjustments.
Need a Methimazole (Felimazole, Tapazole) refill?
RexVet is the first 501(c)(3) non-profit online vet service in the U.S. Talk to a licensed veterinarian by video, get your cats's Methimazole (Felimazole, Tapazole) prescription, and have it shipped through RexVetRx — all for $64.99 per visit.
Book a vet visit — $64.99Methimazole (Felimazole, Tapazole) for Cats
Frequently asked questions
How long does my cat need methimazole?
Methimazole manages hyperthyroidism but doesn't cure it — most cats stay on it for life unless they receive radioactive iodine (I-131) treatment, which can cure the condition.
Methimazole pills or transdermal gel?
Both work. Transdermal gel (applied to the ear) is easier for cats who hate pills, but absorption is more variable. Many vets start with pills and switch if administration is a problem.
Can RexVet refill methimazole?
Yes, for cats with established hyperthyroidism and current bloodwork. RexVet manages chronic refills through RexVetRx via video visit.
What's the cure for cat hyperthyroidism?
Radioactive iodine (I-131) at a specialty facility is curative for ~95% of cats. It's a one-time treatment ($1,500-2,500) that often pays back vs years of methimazole + monitoring.
What if my cat won't take the pill?
Try pill pockets, soft food hiding, or asking your vet about a chicken-flavored compounded liquid or transdermal gel.
Medical review by Dr. Tiffany Delacruz, DVM
Chief Executive Officer & Lead Veterinarian, RexVet. Licensed in Florida, New York, and Virginia.
Last fact-checked: 2026-05-19
Sources
This page is an educational reference and does not replace veterinary advice. Always consult a licensed veterinarian before starting, changing, or stopping medication for your pet.