Antithyroid · For Cats
Tapazole dosage reference for cats (Methimazole)
Veterinary references give this medication as a fixed amount per cat, given every 12 hours, not as a per-kilogram dose, so this guide shows that reference instead of a weight-based calculator. Confirm the product and amount with a veterinarian.
- Onset
- 1-2 weeks for clinical effect
- Duration
- 12 hours per dose
- Class
- Antithyroid
Weight-based calculator estimate from the references listed on this page. This page has not been independently DVM-reviewed — see our methodology .
This information is for educational purposes only. Always consult your veterinarian before giving medication to your pet. Do not use this calculator for emergencies, overdoses, pregnancy, very young animals, very old animals, pets with liver/kidney disease, or pets taking multiple medications.
Sources and review process
Each medication page lists the references recorded for its data. The calculator math and editorial presentation are maintained by PetDosageChart; a page is independently DVM-reviewed only when a named reviewer byline appears. See our methodology and limitations.
Methimazole (often known by brand names such as Tapazole and Felimazole) is an antithyroid commonly used in veterinary medicine for hyperthyroidism, thyroid hormone reduction, and pre-surgical thyroid stabilization. Understanding the dose, monitoring, and potential side effects of Methimazole is critical for your cat’s safety and well-being.
No weight-based calculator on this page: The FDA-approved Felimazole label doses methimazole per cat, not by weight. The starting dose is 2.5 mg every 12 hours. After about 3 weeks, your veterinarian adjusts the dose in 2.5 mg steps based on blood T4 results and how your cat is doing, and monitors kidney values and blood counts, because treating hyperthyroidism can unmask kidney disease. Never adjust the dose at home.
What the source establishes
The starting dose is 2.5 mg every 12 hours. After 3 weeks the dose is titrated to effect from serum total T4 and clinical response, in 2.5 mg steps. The maximum total dose is 20 mg per day divided, not more than 10 mg at once. In the field studies, treatment unmasked kidney disease in some cats. The User Safety section says: wash hands with soap and water after administration, do not break or crush tablets, wear protective gloves for broken or moistened tablets and for litter, feces, urine or vomit of treated cats, and pregnant or nursing women should wear gloves when handling tablets, litter or bodily fluids.
The label doses per cat, not per kilogram, which is why this page shows the 2.5 mg per-cat starting dose instead of a weight-based calculator. Later doses depend on T4 and kidney monitoring by the veterinarian.
FELIMAZOLE (methimazole) Coated Tablets FDA Freedom of Information Summary, NADA 141-292 — Dosage and Administration; Effectiveness, adverse reactions; V. User Safety (approved May 27, 2009).
States that the 2.5 mg and 5 mg coated tablets are dosed in 2.5 mg increments every 12 hours, with a maximum of 20 mg per day divided and no more than 10 mg as a single administration.
A regulatory announcement summarizing the approved labeling. It is not a treatment plan for an individual cat.
FDA CVM Update: first generic methimazole coated tablets for hyperthyroidism in cats — Dosing paragraph (updated July 22, 2025).
Methimazole Starting Dose for Cats
| Cat weight | Reference amount (every 12 hours) |
|---|---|
| Any weight | Starting dose 2.5 mg per cat (FDA label); your veterinarian then adjusts it in 2.5 mg steps based on T4 and kidney monitoring |
Veterinary references list this amount per cat, not per pound. Give only the amount and schedule your veterinarian prescribes.
The label’s maximum is 20 mg per day, divided into doses of no more than 10 mg each. Your cat’s dose is whatever your veterinarian prescribes after testing.
By Weight
Tapazole reference by cat weight
Choose a common weight to open its optional reference page. Return to the main guide for the per-cat reference amount.
Common-weight pages are convenience views of the same educational reference, not separate medical recommendations.
How to Give Methimazole to Your Cat
Give methimazole tablets whole, by mouth. Do not split or crush Felimazole coated tablets: the FDA-approved label says not to break or crush them. Wash your hands with soap and water after giving a dose and after cleaning the litter box, and wear gloves for contact with broken or moistened tablets, litter, vomit or urine. People who are pregnant, may become pregnant, or are nursing should wear gloves when handling tablets, litter or the cat’s bodily fluids, because methimazole can harm a developing baby and passes into breast milk. If your cat cannot take tablets, ask your veterinarian about prescribed alternatives such as a compounded transdermal gel for the inner ear flap (wear gloves and rotate ears) or a compounded liquid. Consistency in timing is important for thyroid control.
It is generally recommended to give Methimazole with food to help reduce stomach upset. It may interact with anticoagulants (warfarin), digoxin, phenobarbital, and other hepatotoxic drugs.
Side Effects and Safety
Common side effects include vomiting, loss of appetite, lethargy, and facial itching and scratching. More serious side effects can occur, such as liver toxicity (jaundice), bone marrow suppression, bleeding disorders, and severe skin lesions.
Cautions · 12
When Tapazole should be used with caution or avoided
Some cats should not take Tapazole, or need a different dose and closer monitoring. Tell your veterinarian about your pet's full health history and every other medication or supplement they take before giving Tapazole.
- liver disease
- autoimmune disease
- known hypersensitivity to methimazole
- pregnancy
Interactions · 13
Tapazole drug interactions
Tapazole can interact with other drugs. This list is not complete — always give your veterinarian a full list of your cat's medications and supplements.
Reference Limits · 14
When this reference is not enough
A reference table cannot decide whether a product or treatment is appropriate for an individual animal. Do not rely on it in these situations — talk to your veterinarian instead:
- In an emergency, or after accidental ingestion or a suspected overdose
- For pregnant or nursing pets
- For very young or very old cats
- For pets with liver disease, kidney disease, or another chronic illness
- For pets taking several medications at once
- When you are not sure of your cat's current, accurate weight
- For combination products that contain additional active ingredients
Overdose · 15
Suspected overdose: what to do
If you think your cat had too much Tapazole, or swallowed any medication by accident, act right away. Do not wait for symptoms to appear.
- Call your veterinarian or the nearest emergency animal hospital.
- ASPCA Animal Poison Control Center: (888) 426-4435
- Pet Poison Helpline: (855) 764-7661
A consultation fee may apply to the poison hotlines. Have the medication packaging ready, and note how much your pet may have taken and when. Do not try to make your pet vomit unless a veterinarian tells you to.
When to Call the Vet
If your cat experiences any of the following, contact your veterinarian or an emergency clinic immediately:
- Yellowing of the gums or skin (jaundice)
- Persistent vomiting or refusal to eat for more than 24 hours
- Unusual bleeding or bruising
- Severe facial itching or scratching at the face and neck
- Lethargy or collapse
Frequently Asked Questions
Frequently Asked · 07
Questions about this medication
How long does a cat need to take methimazole?
Can methimazole cause kidney problems in cats?
Is the transdermal methimazole gel as effective as tablets?
How often should thyroid levels be checked on methimazole?
What happens if I miss a dose of methimazole for my cat?
Sources · 09
Sources & references
The structured medication record behind this page names the references below. The links open the publisher or official resource; they do not turn this page into a prescription for an individual animal.
- FELIMAZOLE (methimazole) Coated Tablets FDA Freedom of Information Summary, NADA 141-292
Dosage and Administration; Effectiveness, adverse reactions; V. User Safety (approved May 27, 2009). Supports the specific claim described above; it is not a review of the entire page.
- FDA CVM Update: first generic methimazole coated tablets for hyperthyroidism in cats
Dosing paragraph (updated July 22, 2025). Supports the specific claim described above; it is not a review of the entire page.
- Plumb's Veterinary Drug Handbook — listed in this medication's source record.
- Merck Veterinary Manual — listed in this medication's source record.
- DailyMed label search for Methimazole — check current product and formulation labels; some veterinary uses may be off-label.
Specific citations above support the identified claims. Other source names remain record-level references; further claim review is still needed. Read our methodology and limitations.
Transparency · 11
How this page was made
This page's structured medication record includes Plumb's Veterinary Drug Handbook among its source names. This medication is presented with its per-animal reference amount instead of a weight-based calculator. A source record is not the same as an individualized prescription or an independent clinical review.
- Sources cited
-
- Plumb's Veterinary Drug Handbook
- Merck Veterinary Manual
- Calculator formula
- No weight-based calculator is shown because veterinary references give this medication as a fixed amount per animal rather than per kilogram. Use the exact amount directed by the veterinarian.
- Editorial owner
- Prepared and maintained by the PetDosageChart editorial team, a software-led publisher and not a veterinary practice.
- DVM review status
- Not independently DVM-reviewed. A named reviewer and review date appear here only after a confirmed review.
More on our methodology and editorial process — how we source, calculate, and review cats dosage data.
Safety · 10
More resources
- Pet Medication Safety Hub — What's safe, what's dangerous, and emergency signs
- How we calculate dosages — Our sources, math, and review process
- Printable emergency checklist — One-page reference for your fridge or first aid kit