Felimazole (thiamazole) is the most commonly prescribed medication for feline hyperthyroidism, a condition affecting approximately 10% of cats over the age of 10. Since it is a lifelong daily medication, the cumulative cost is significant, making it one of the medications where buying with a prescription saves the most money.

Price Comparison: Felimazole 2.5mg (100 tablets)

  • From your vet: £55–£80
  • Online pharmacies: £30–£45
  • Saving per pot: £20–£40

Most hyperthyroid cats need 1–2 tablets twice daily, so 100 tablets lasts roughly 25–50 days. Over a year, buying from an online pharmacy instead of the vet saves £150–£300.

Felimazole 5mg Prices

Some cats are stabilised on the higher-strength 5mg tablets:

  • From your vet: £65–£95
  • Online pharmacies: £40–£55

Generic Alternatives

Generic thiamazole tablets are available for cats, though they are less commonly stocked by online pharmacies than the branded Felimazole. Vidalta (carbimazole, a pro-drug that converts to thiamazole in the body) is another option that offers once-daily dosing, but it tends to be more expensive per day of treatment.

Monitoring Costs

Cats on Felimazole need regular blood tests to check thyroid levels and kidney function:

  • First 3 months: Blood tests every 2–4 weeks until stable (£80–£150 per test)
  • Once stable: Blood tests every 3–6 months (£80–£150 per test)

These monitoring costs are in addition to the medication costs. Annual monitoring typically costs £300–£600 in blood tests and consultation fees. This is an area where comparing vet prices can make a meaningful difference.

Total Annual Cost of Managing Hyperthyroidism

  • Medication (buying at vet): £400–£700
  • Medication (buying online): £220–£400
  • Monitoring blood tests: £300–£600
  • Prescription fees: £30–£50 (two per year)
  • Total (buying online): £550–£1,050 per year

This is why hyperthyroid cats are one of the cases where prescription savings make the biggest difference to owners' wallets.

Last updated: March 2026. Sources: VetCost pharmacy price data, International Society of Feline Medicine.