I have found a ton of medical papers about methimazole. I have found a ton of medical papers about levothyroxine. I have found a ton of medical papers about thyroidectomy. What I cannot find is any layman-parsable statement of how methimazole works, and whether that function still has any effect on someone whose thyroid has been removed. I am curious because people who have hyperthyroid cats often treat with methimazole, but have to be careful not to let it touch their skin. But f said person doesn't have a thyroid, do they need to be as careful about not touching the methimazole? Does it affect only the thyroid itself, or does it bind to the hormone produced before the rest of the body does?

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    While I agree with the answer given (upvoted), I would also read about any possible adverse reactions. While someone who might have had a total thyroidectomy (no one is born without a thyroid gland. That's lethal in utero) doesn't have to worry about the drug affecting their replacement therapy, some drugs have serious adverse reactions which are idiosyncratic in nature and not dose related, which can be lethal. Mar 9 at 2:31

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If you want to understand how a drug works, a helpful phrase is "mechanism of action". Pairing that keyword with the drug you mentioned, the first Google result is this one:


The primary mechanism of action of methimazole is to block thyroid hormone production from the thyroid gland. It interferes with the step that causes the iodination of tyrosine residues in thyroglobulin, mediated by the enzyme thyroid peroxidase, thus preventing the synthesis of thyroxine (T4) and triiodothyronine(T3).

However, this drug does not affect the existing thyroxine (T4) and triiodothyronine (T3) in the circulation or stored in the thyroid gland. Similarly, there have been no observations of alterations in the effectiveness of exogenously administered thyroid hormones.

That said, I would not recommend anyone ignore warnings in the instructions for use of some drug without consulting with their doctor, and it seems very unlikely to me that this specific set of circumstances has been tested because there are no medical benefits to being less careful with your cat's drugs.

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