I had exactly this. The welts seemed to appear mostly at night. Taking an anti-histamine (Zyrtec) after dinner helped prevent them or at least reduce the itching and redness. There’s no way I could have slept without the Zyrtec, so even though it’s not fun to be on multiple drugs, the benefits of taking an anti-histamine seem to outweigh the costs. After a week, I tapered off the Zyrtec and after about two weeks, the itching completely went away. My methimazole dosage changed from 30mg to 20mg over the course of these two weeks; that might have helped, or maybe my immune system just adapted.
