Can starting or stopping methimazole cause rashes on your body?

Yes. Methimazole can cause a rash in the body. Hyperthyroid can also cause a rash in the body so starting or stopping this medication can cause rash.
Yes. One of the well-known side effects of Methimazole is an itchy, scaly skin rash that ocurrs in about 10% of patients. Talk to your doctor. You may be able to take ptu (propylthiouracil) without the rash, but it can cause it as well.