reasons for abnormal thyroid hormone levels will depend on what the cause of the intrinsic thyroid disease is to begin with. in hashimoto's thyroiditis where the body makes antibodies against the thyroid gland levels of circulating thyroid hormone may vary depending on the status of the hashimoto's disease. in grave's disease patients can vary from overactive to underactive thyroid hormone over time. in people with thyroid nodules determining whether the growth(s) on the thyroid gland are malignant or not may account for variations in thyroid hormone levels. in people for whom a medicine such as lithium is suppressing the circulating levels of thyroid hormone levels may vary depending on the use of lithium. lastly in people with dietary deficiencies of iodine production of thyroid hormone can be affected. thyroid hormone is at best a weak treatment for depression and low thyroid hormone is usually "the" explanation for depression only when tsh levels are extremely high. in someone without existing thyroid disease i would not attach a lot of importance to thyroid hormone levels unless the tsh level was very much higher than 10.
twice in the last 5 yrs my thyroid medication totally quit working. why would this happen? my depression is unbearable.