This patient support community is for discussions relating to thyroid issues, goiter, Graves disease, Hashimoto's Thyroiditis, Human Growth Hormone (HGH), hyperthyroid, hypothyroid, metabolism, pituitary gland, cancers, thyroiditis, and thyroid Stimulating Hormone (TSH).
Graves Disease is an autoimmune disease which produces antibodies that attack your thyroid, causing it to overproduce the thyroid hormone T4. Methimazole is an anti-thyroid drug, that works to block production of T4 by the thyroid. If you take too much, you can become hypothyroid (underactive) which causes many of the symptoms you describe.
Often, patients are started at a higher dosage of Methimazole to bring hyperactivity under control. Frequent blood tests should be done to ensure that it isn't working too well. Many people who start at a higher dose then have reductions of dosage until a "maintenance" level is found. I started at 30 mg of Methimazole daily, had it reduced to 15 mg, then 10 mg, then we tried no dosage for a couple of weeks, before I ended up taking 10 mg one day and 5 mg the next for several months until I chose to have my thyroid removed.
Call you doctor, and ask to be tested if you haven't been recently. The only other thought I have is maybe Methimazole isn't the treatment for you (there are other anti-thyroid drugs) - if you continue to feel bad despite changes in dosage, it might be time to consider RAI or TT.
Good luck!