Felimazole for Cats
Hyperthyroidism Treatment
Twice-daily methimazole tablets for overactive thyroid. The original feline anti-thyroid drug. Save up to 50% buying online.
Buy Felimazole at UK pharmacy prices
UK registered pharmacies dispense the same Felimazole your vet prescribes, often for less. Ask your vet for a written prescription (capped at £21 under the CMA Order, from 2027), then fill it online.
Affiliate link to The Pharm Pet Co., a UK registered veterinary pharmacy. We may earn a small commission, at no extra cost to you. Always follow your vet's guidance on medication choice and dosing.
What is Felimazole?
Felimazole is a veterinary-licensed formulation of methimazole (thiamazole), manufactured by Dechra. It is the original and most widely used anti-thyroid medication for cats in the UK, prescribed for the management of feline hyperthyroidism.
Methimazole works by inhibiting thyroid peroxidase, the enzyme responsible for incorporating iodine into thyroid hormones. This reduces the production of T3 and T4 hormones, bringing levels back to normal and controlling the symptoms of hyperthyroidism including weight loss, hyperactivity, increased appetite, vomiting and rapid heart rate.
Felimazole comes as small sugar-coated tablets in 1.25 mg and 2.5 mg strengths. The small tablet sizes allow precise dose adjustments, which is particularly important during the initial stabilisation period. Unlike Vidalta, Felimazole is given twice daily (every 12 hours), though this allows more precise control of thyroid levels.
Felimazole Dosage
Starting Dose
2.5 mg twice daily (5 mg total per day). Given as one 2.5 mg tablet morning and evening, approximately 12 hours apart. Can be given with or without food.
Dose Adjustment
After 3 weeks, blood T4 level determines dose changes. May be increased in 1.25 mg increments up to 10 mg twice daily (20 mg/day). May be decreased if T4 drops too low. Precise adjustments are a key advantage of Felimazole over Vidalta.
Available strengths: 1.25 mg and 2.5 mg sugar-coated tablets. The small sizes allow dose increments of 1.25 mg for fine-tuning.
Side Effects & Warnings
Common (10-20%)
- • Vomiting and nausea
- • Reduced appetite and weight loss
- • Lethargy
- • Mild self-limiting diarrhoea
Serious (Rare but Important)
- • Facial excoriation (severe scratching)
- • Bone marrow suppression
- • Hepatopathy (liver damage)
- • Immune-mediated haemolytic anaemia
Critical Warning
Human handling: Methimazole can be absorbed through the skin and may affect human thyroid function. Pregnant women should NOT handle crushed or broken Felimazole tablets. Always wash hands after giving tablets. Wear gloves if tablets are split.
Felimazole Price Comparison
Felimazole 1.25 mg — 100 tablets
Felimazole 2.5 mg — 100 tablets
Felimazole 2.5 mg — 200 tablets
Alternatives to Felimazole
Vidalta (Carbimazole)
Once-daily sustained release. More convenient but less precise dose adjustment. See our Vidalta guide.
Radioiodine (I-131)
Curative single injection. £2,000-£3,000 one-off cost eliminates lifelong medication. Over 95% success rate. The gold standard treatment.
Hill's y/d Thyroid Care Diet
Iodine-restricted diet. No medication needed but must be the sole food source. Less effective than medication but avoids tablets.
Frequently Asked Questions
Treating hyperthyroidism in cats. Given twice daily to block excess thyroid hormone production.
£0.40-£1.00 per tablet at the vet, £0.20-£0.55 online. Significant savings buying online for this lifelong medication.
Felimazole (methimazole) is twice daily. Vidalta (carbimazole) is once daily. Both equally effective. Felimazole allows finer dose adjustments.
Vomiting and appetite loss in 10-20%. Facial scratching, bone marrow suppression and liver issues are rare but serious. Regular blood tests essential.
Yes. T4, kidney function and blood count at 3, 6, 10 weeks then every 3-6 months for life.
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Save on Felimazole
Lifelong thyroid medication is expensive. Buy online and save £100-£200+ per year.