A wide range of supplements that claim to support or improve thyroid function are available online and in retail stores. Some list only herbs as ingredients. Others are capsules filled with dried, ground-up thyroid gland from pigs or cows.
When a number of his patients told him they were taking the supplements, endocrinologist Victor Bernet, MD, of the Mayo Clinic, Jacksonville, Fla., became curious. Might they contain the same thyroid hormone as Levothroid, Levoxyl, Synthroid, Unithroid and other prescription drugs used to treat thyroid hormone deficiency?
Yes, Bernet says - and it’s risky. "Even a little too much T4 can give a person palpitations, could give atrial fib and blood pressure issues and such," he tells WebMD. "We have people coming in feeling nervous, can't sleep, decreased exercise tolerance, hearts running overtime."
T4 (thyroxine) is the active ingredient in Synthroid and other prescription drugs used to treat thyroid deficiency.
Bernet and colleagues tested 10 different supplements, selected because they appeared to be the most popular products sold for "thyroid support." Five of the products listed animal thyroid gland as an ingredient, five did not.
The result: nine of the 10 pills contained T4. At the dose recommended on the label, four of the pills delivered T4 at doses ranging from 8.6 to 91.6 micrograms per day. A typical daily dose of prescription T4 is 50 to 150 daily micrograms, Bernet says.
Nine of the supplements carried another thyroid hormone, triiodothyronine, or T3. Five delivered daily T3 doses of more than 10 micrograms per day. "That's more than half of what the body would normally make in a day," Bernet says.
"Thyroid hormones are medications that should be bought only under prescription," Bernet tells WebMD. "I do not recommend anyone take any of these supplements. ... This is a general warning to patients that 90% of those products we randomly picked have clinically significant amounts of thyroid hormone."
Thyroid Support Supplements Legal
The supplements are legal as long as they aren't spiked with pharmaceutical drugs, according to federal law. That law, passed in 1994, permits the sale of "a dietary substance for use by man to supplement the diet by increasing the total dietary intake (e.g., enzymes or tissues from organs or gland)."
Firms that sell the supplements are responsible for "determining" that their products are safe and that claims made about them "are substantiated by adequate evidence to show they are not false or misleading." But the law exempts these supplements from having to be approved by the FDA.
"Thyroid support supplements have been around for a long time," Duffy MacKay, ND, vice president for scientific and regulatory affairs for the Council for Responsible Nutrition (CRN), tells WebMD. CRN is the trade group that represents the supplement industry.
"The presence of desiccated glands in dietary supplements is perfectly legal," MacKay says. "The amounts of hormone in the product should reflect what naturally occurs in the [animal] gland itself. ... These are not extremely high levels of thyroid hormone."
But MacKay says his comments are limited to firms "following the rules." He condemns "spiked products masquerading as supplements."
The FDA did not respond to WebMD's request for comment on the Bernet study findings.
Bernet says thyroid support products should be more tightly regulated. MacKay says Bernet is entitled to his opinion, but that if he wants things changed he should write to his congressman to seek a change in federal law.
However, MacKay and Bernet fully agree on at least one major point: Anyone thinking of taking a thyroid support supplement should talk with a medical professional, and should be sure to tell all of their doctors what they are taking.
Bernet reported the study findings in a presentation to the annual meeting of the American Thyroid Association, held Oct. 26-30 in Indian Wells, Calif.