Over-the-counter nutritional supplements aimed at "thyroid support" promise to boost metabolism, increase energy, and improve mood. A new study finds that some of the supplements aren't the herbal remedies they purport to be. Nearly all of the supplements tested contained thyroid hormones. These hormones – T4 and T3, officially called thyroxine and triiodothyronine – are usually available only by prescription and can cause major side effects.
Researchers tested the contents of 10 common thyroid supplements available online. Nine of them, they found, contained at least one hormone, and five contained both. Several of the products also contained as much or more of the hormones as a doctor would prescribe to treat hypothyroidism (the condition in which a person produces too little thyroid hormone). One sample had close to four times the levels of T4 that would be the starting dose of a prescription medication. Even for people with diagnosed hypothyroidism, getting the dosage right can be tricky; differences between one T4 prescription pill dosage and the next are often about 12 micrograms. "People are so sensitive that small changes like that can cause big differences," says Dr. Victor Bernet, the chair of endocrinology at the Mayo Clinic Florida.
While low levels of the hormones can lead to joint pain, depression, weight gain, and heart disease, too much thyroid hormone can lead to difficulty sleeping, tremors, restlessness and trouble concentrating, and even heart problems and thinning bones.
Lately, researchers have discovered that, for a number of supplements, the contents of the pill don't match the ingredients on the label. In one recent study, 80 percent of companies tested sold products with fillers, substitutes, and contaminants; another study found a meth-like substance in a common workout supplement. The bottom line: Proceed with caution when taking any herbal supplements. Ask your doctor about the supplement you take and be sure to look for an NSF, USP, or ConsumerLab.com seal on the bottle.