There are a number of symptoms associated with low thyroid levels, such as changes in the menstrual cycle, depression and constipation, according to WebMD. Dry hair, dry skin, fatigue, sensitivity to cold and a slow heart rate are also associated with low thyroid levels. Swelling of the thyroid gland, unexplained weight gain and carpel tunnel syndrome may also indicate that a person has low thyroid levels. The main treatment for this condition is a synthetic thyroid hormone called T4, which thyroid patients take every day. Regular blood tests are also performed to test the thyroid levels in the body.