The thyroid hormone levothyroxine is one of the most commonly prescribed drugs in the country. With so many people needing to take thyroid hormone, most doctors think they know all about it. But scientists are still discovering fascinating new information about treating hypothyroidism, including whether or not some people need to take T3 thyroid hormone as well as T4.
Doctor Says T3 Thyroid Hormone Is Too Dangerous:
Q. My niece is a doctor. Since thyroid problems run in our family, we asked her about T3 for thyroid. She says it is very dangerous. T3 only lasts in your system for half an hour and gives you a high. If you have heart problems, too much can give you a heart attack.
She doesn’t know of any evidence demonstrating that anyone is unable to convert T4 to T3, so regular Synthroid should work for everyone.
How Thyroid Hormones Work:
A. The thyroid gland produces both T4 (levothyroxine) and T3 (triiodothyronine). Only T3 is active in body tissues and is responsible for cellular metabolism. The body makes T3 from T4 by removing one iodine atom with an enzyme right in the tissue where the hormone is needed.
As your niece said, many people with sluggish thyroid glands do well on just levothyroxine (Levoxyl, Synthroid, Tirosint, Unithroid). She is not completely up to date on her information, however. Some individuals (perhaps as many as 15 percent) have a genetic variation that can influence the efficiency of T4 to T3 conversion (Endocrine Connections, Dec., 2015). While these people can get by with T4 alone, they may not feel good.
How Can You Tell If You Need T3 Thyroid Hormone?
Doctors often assess thyroid function with TSH (thyroid stimulating hormone). This is a brain hormone that tells them whether the pituitary gland is trying to get the thyroid to work harder, suggesting that blood levels of T4 thyroid hormone are low. That is why a high TSH (exactly how high is controversial) indicates low thyroid function.
Using TSH as the standard measure of thyroid function won’t always show what is happening with T3 thyroid hormone, however. For that, more detailed blood tests are needed. To find out if you are one of the people with a genetic variation affecting T4 to T3 conversion, a special test is required that is not widely available. You will find far more detail about this topic and why some doctors prescribe T3 along with T4 in our downloadable 25-page Guide to Thyroid Hormones, available at PeoplesPharmacy.com.
Too much T4 or T3 thyroid hormone can indeed lead to heart problems or anxiety and insomnia. That’s why it is so critical to get thyroid hormone doses adjusted properly. But despite what your niece told you, people don’t get “high” on T3 thyroid hormone as they would on alcohol, marijuana or other drugs of abuse.
