Levothyroxine 50 MG 100 Mg is used to treat an underactive thyroid gland. Thyroid hormones are produced by the thyroid gland and aid in regulating growth and energy levels. Thyroxine, the thyroid hormone that is absent, is replaced with levothyroxine. The thyroid gland ordinarily produces thyroid hormone, which it either replaces or increases. Levothyroxine 50 MG 100 Mg is also sued to treat other forms of thyroid problems. Infertility should not be treated with this drug unless it is brought on by low thyroid hormone levels.