My sister had an overactive thyroid, hyperthyroidism, due to the fact that she had graves disease, an autoimmune disorder. The doctors seemed to think this can be triggered by a stressful "life event". Interestingly, she had just had a baby. She took beta blockers and so many other meds which got this all under control manually and then when she got pregnant again, the hyperthyroidism/graves disease came back. She decided to take a more drastic approach and was medicated with radioactive iodine which killed the thyroid gland. This was about 6 years ago and since then, she has had another baby (at 43). This little boy is now 4 and she has had no reoccurrence of the disease. How fantastic is modern medicine!