Liothyronine is the generic name for the drug that is a synthetic version of triiodothyronine, the thyroid hormone abbreviated as T3.

Most commonly, this drug is a treatment that is added to levothyroxine. Thyroid cancer patients who are withdrawn from levothyroxine in order to get an accurate diagnostic scan may also receive this drug to help counteract the hypothyroid effects of lack of levothyroxine.

Some alternative practitioners also believe in using liothyronine-only therapy as a treatment for hypothyroidism, hypometabolic conditions, and the controversial "Wilson's Syndrome."

Pharmaceutical names

Triiodothyronine, liothyronine, liothyronine sodium

Hormone content

T3 only

Uses

Usually in combination with synthetic T4; occasionally, as a treatment in itself. Some people don't respond well to synthetic T4 or even to desiccated thyroid. Most of these people eventually respond to T3 either in combination with desiccated thyroid or by itself.

Dietary considerations

Cytomel (and possibly the other brands) contains lactose as a filler.

When taking both synthetic T4 and T3 as separate pills, the ratio of T3 to T4 can be controlled. However, the absorption of T4 is so variable (from 40 to 72 percent) that the ratio cannot be said to be constant.

Occasionally, T3 is used as a treatment in itself. Other advantages For many patients, taking T3 in addition to T4 has relieved the symptoms of hypothyroidism that wouldn't disappear on T4 alone.

A large body of research supports the use of T3 in addition to T4 for hypothyroid patients. Other disadvantages T3 is faster-acting than T4, so patients sometimes spread out their dose and take it two or more times a day to avoid having their energy levels crash when the effects of T3 wear off.

Although lab results may not indicate a problem, even a combination of synthetic T4 and T3 sometimes doesn't alleviate all of the symptoms of hypothyroidism.

Pure T3 cannot be used by itself during a pregnancy. Much of the pregnancy fetus depends on a good supply of T4.

Those taking synthetic T3 with T4 need to take two types of pills and have two prescriptions filled instead of just one.

Some brand names

Cytomel (Canada and the US), Tertroxin (the UK), Cynomel (France)