Should I take Cytomel if I have hypothyroidism?

Hypothyroidism means an under-active thyroid.  In hypothyroidism, the thyroid gland is making too little thyroid hormone, and treatment involves giving a person thyroid hormone in pill form to replace what the body is not making. 

There are two major forms of thyroid hormone.  One is thyroxine, usually referred to as “T4” because chemically it contains 4 iodine atoms.  The most common form of medication for hypothyroidism is levothyroxine (brand names Synthroid, Levoxyl and others) which is T4.  The other major form of thyroid hormone is triiodothyronine, commonly called “T3” because chemically it contains 3 iodine atoms.  The prescription drug Cytomel (generic name liothyronine) is T3, and it too can be used to treat hypothyroidism. 

In most cases, people are given T4 alone to treat hypothyroidism.  There are several reasons for this.  T4 is longer-lasting in the body than T3, so blood levels do not vary much with once daily dosing, whereas blood levels fluctuate more with the shorter-acting T3.  In addition, the body can chemically convert T4 to T3 by removing one iodine atom, so in theory there is no need to give T3 separately.  On the other hand, there have been a number of studies suggesting that people feel better when they are given both T3 and T4, and in my own personal experience this sometimes, though far from always, makes a difference. 

This relatively simple question-whether to use T3 as part of the treatment for hypothyroidism-is the source of major controversy.  Most professional organizations that set guidelines for treating hypothyroidism argue against using T3 except in relatively rare circumstances.  On the other hand, most real-world endocrinologists such as me encounter many people who do not feel as good on T4 treatment alone as they felt before they developed a thyroid problem.  In those individuals, I will consider a trial of T3 in combination with T4, though if it proves of no greater value than T4 alone, I stop it and go back to the T4-only treatment.  Some of my colleagues think that this is a bad approach and will not prescribe T3, but my goal is to help my patients feel better, and I think combination T3 and T4 therapy, as with Cytomel and Synthroid, is safe provided blood tests are being done and the person is being monitored for side effects.

Cytomel (liothyronine) is a thyroid hormone commonly prescribed to treat hypothyroidism. T4, thyroid hormone, is prescribed to patients diagnosed with hypothyroidism and is taken in a single dose everyday for the rest of their life to compensate for a underproduction of thyroid hormone by the body. As with any medication, Liothyronine may cause some side effects and you should consult your physician if you experience any discomfort.