As you stated, methimazole is a medication that is used to help people that have hyperthyroidism. It acts by decreasing the amount of active thyroid hormone levels in the body. It is also true that people that have too much thyroid hormone (such as yourself) are more likely to lose weight than gain weight. The reverse is true (people with low thyroid are more likely to gain weight). Thus, anyone that is placed on this medication is likely to gain weight. The important question is if you are getting too much f the methimazole. The answer to that question lies in the blood test for the thyroid stimulating hormone (TSH test). The TSH test is done to see if someone is hyperthyroid or hypothyroid (too little thyroid hormone). Your TSH when you were hyperthyroid was too low. Now that you are on methimazole, it will be higher. You just have to make sure that you and your endocrinologist
haven't overshot and caused hypothyroidism (with a high TSH). The only way to find this out is to get it tested. If your TSH is normal, then the methimzole dose is correct and should not be adjusted. Only your endocrinologist will know the answer to this question. I suggest that you schedule an appointment to work out these issues.