Weights loss as a side effects of thyroxine use - how much is too much?

When TSH is low. People who take thyroxine for simple hypothyroidism should have normal TSH to be safe. They should not loose weight, unless their prior weight gain was due to hypothyroidism. Taking too much thyroxine can cause atrial fibrillation and osteoporosis. On the other hand people with thyroid cancer are sometimes given a slight excess of thyroxine to prevent the cancer from returning.