Liothyronine sodium is a man-made, or synthetic, version of a thyroid hormone called triiodothyronine, or T3. The thyroid gland, situated in the neck, makes T3 in small quantities together with another thyroid hormone, tetraiodothryonine, or T4. T4 is an inactive hormone that is produced in greater amounts, and it is converted into T3, which is active, in various body tissues, where it regulates important functions such as the metabolic rate. In the disease known as hypothyroidism, there is a lack of thyroid hormones, leading to symptoms such as dry skin, feeling the cold and decreased energy. Treatment of hypothyroidism involves replacement of the missing natural hormones with synthetic versions, and liothyronine sodium is sometimes used for this purpose.
When thyroid function is abnormal, and a person develops hypothyroidism, the most common synthetic hormone used to treat the condition is typically levothyroxine sodium, a manufactured copy of the T4 hormone. Alternatively, some people will take a combination of T4 and liothyronine sodium, or T3, and some may be prescribed liothyronine sodium on its own. There is scientific controversy regarding whether the combination treatment offers benefits over taking T4 alone. Some patients maintain that only taking T3 and T4 together makes them feel well, but so far scientific studies have failed to prove that the combined treatment is superior, and it is possible that the effect might only apply to specific individuals.
T3 peaks in the blood two to three hours after taking it, so it is administered two or three times a day, while T4 is only taken once a day. With T4, blood levels are more steady and there is thought to be less risk of too high levels occurring, which could lead to symptoms of hyperthyroidism such as palpitations, sweating and diarrhea. T3 might be preferred if there is a need to increase blood levels more quickly, for example, in more serious cases of thyroid suppression or in cases where the thyroid gland has been removed. Liothyronine sodium may also be used in emergencies where there is so little thyroid hormone that the person is in a coma and a rapid rise in hormone levels is essential.
Some people purchase liothyronine sodium for use as a fat-burning supplement, or bodybuilding supplement, because of its effects in speeding up the metabolism. As this generally means that the drug is being taken without the blood levels being closely monitored by a doctor, there is a risk of overdose occurring, resulting in symptoms such as irregular heartbeats, insomnia, headaches, muscle cramping and diarrhea. In extreme cases there is the possibility of a life-threatening condition developing, known as a thyroid storm, where a very high temperature and fast heart rate may lead to coma and death. Adverse effects of liothyronine sodium can be prevented by following a doctor's treatment plan, together with regular blood tests to check hormone levels.