Your weight gain may be related to too much methimazole causing your Free T3 and Free T4 to be too low, and causing you to become hypothyroid. Have you been tested for Free T3 and Free T4? If so, please post results and reference ranges shown on the lab report. If not, then you should insist on both tests.
I was diagnosed with graves disease in october have gained 15 pds since. I lost weight sold all my cloths now nothing fits I take 20mlg methimazole I eat healthy and still no control over the weight gain very sad
Everyone is different when it comes to medications and their thyroid disease-though weight loss is more common of Graves' disease, some people gain, just like some people lose weight being hypo.
I was on 5 of methimazole myself when diagnosed with Graves', and gained 15lbs. For me, it was much needed-I had lost nearly thirty pounds in just a few short months being un-medicated.