The American Thyroid Association doesn’t recommend the use of thyroid hormones as a weight loss tool.  Although excess thyroid hormone treatment has been shown to help with weight loss in the short term, the weight is usually regained when the treatment ends. There have been negative repercussions, too, and patients have been found to lose muscle along with body fat.  The conclusion is that thyroid hormone treatment has no significant long-term effect on weight loss and may cause other metabolic problems.