My cat on Tapazole has skin sores and hair loss. Is it a side effect?

These signs could be consistent with methimazole related side effects. GI upset and facial itching are some of the most common acute side effects in the first few months of therapy. I would recommend stopping the medication until you can talk to your vet about your concerns. Some cats can not take this medication and thus require an alternate method of treatment. If still eating and drinking that is good. If any of the symptoms worsen an ER visit is advised. I hope this helps and thank you for using Petco Pet Education Center, formerly Petcoach!

If you are having trouble getting the thyroid under control, you may look into the prescription diet Science Diet Y/D. This diet works well for a lot of cats and eliminates the need for medication. You can also discuss permanent treatment such as radioactive iodine therapy. The hair loss could be due to other causes however. I recommend to call you veterinarian for next steps. Best of luck.

Poor Tora! This hair loss could be due to a skin or fungal infection, fleas, mites, allergies, or endocrine disorder. Having her seen by a vet tomorrow is a good idea, as the vet can diagnose the cause and can treat her. Best of luck.

Thanks for posting on the forum! Focal alopecia (hair loss) can be a sign associated to different skin diseases. The most common are: dermatophytosis (fungal infection), scars, medication application site, demodicosis (parasitic infection) alopecia areata (uncommon), behavioral problems i.e. stress leading to excessive licking and grooming. I would suggest to have her checked by your veterinarian as further test are needed to make a diagnosis and prescribe the correct treatment, if needed. I do not recommend to proceed with the shampoo without an examination first. Your vet might perform a skin scrape to check for parasite and collect a sample to exclude a fungal infection; further test might be needed depending on the results of the ones mentioned. 
Do not hesitate to post again on the forum or request a consultation if you would like to discuss it any further.

If you have ruled out fleas/skin mites. I recommend to have him tested for hyperthyroidism and if that's not the cause, have him on a 12 week food trial with a hydrolyzed protein diet. You must start moving down the list of potential causes of the skin lesions. Atopy is still on the list but is harder to test for so rule out these other causes first. Best of luck and please feel free to post any additional questions.

Hello and thank you for contacting Petco Pet Education Center, formerly Petcoach. It may be Demodex infestation - a skin parasite that may be present in indoor-only cats. Please, take Tonks back to your vet to examine skin scrapes under the microscope and possibly to change treatment she is currently receiving.

Hi, thanks for using Petco Pet Education Center, formerly Petcoach! Poor Ginger! It isn't serious but it is a complication of some of the topicals. It likely will happen with the 2nd dose too so you may want to consider the other option your Vet provided. I hope this helps and I wish Ginger the very best!