Felimazole is the trade name for Thiamazole. Controls production of thyroid hormones. Very useful in hyperthyroidism in cats which is a common condition of middle aged to older cats. Can be once or twice daily dosing.

There are a whole lot of ill-effects noted and you do see them; vomiting, off food, lethargy, severe skin irritation, jaundice, bleeding, changes in blood picture (reduction in both red and white cells). All in all this is a drug to use with care, but what a boon it is in over-active thyroid cases. Where it is well tolerated it is excellent treatment.

If your cat is put on the drug then just stop it and report to the veterinarian if you see any ill-effects.

Cats with over-active thyroids have increased blood pressure. When treatment is initiated the reduction in blood pressure can reveal kidney trouble which was present before, but which was counter-acted by the increased blood pressure allowing the kidneys to keep the bloodstream cleaner than at normal blood pressure. However increased blood pressure is always bad in the long run so this should not stop us using treatment.