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WASHINGTON — Manufacturers of some dietary supplements have been using a stimulant in their products while falsely claiming it is a dietary ingredient, the Food and Drug Administration said Monday, as it announced new steps to crack down on the practice.

The ingredient, methylsynephrine, acts similarly to amphetamine. It was first developed in Europe, and is not approved in the United States as either a drug or a dietary supplement.

The World Anti-Doping Agency, the international group in charge of fighting the use of drugs in sports, has banned the ingredient — also known as oxilofrine — from use in competitive games. Michael Kopech, a Red Sox pitching prospect, was suspended for 50 games last year after testing positive for the stimulant, although he insists he didn’t knowingly take it.


But the ingredient has been easy to buy, or order online, in the United States and is advertised for weight loss and bodybuilding. Now, the agency is warning the makers of dietary supplements that contain the stimulant to pull their products off the market.

“Our hope and our belief is that is this is a strong enough action that it is going to send an industry-wide message, that no company should be under the illusion that methylsynephrine is a dietary ingredient that could be marketed legally as a dietary supplement,” said Steven Tave, acting director of the FDA’s Office of Dietary Supplement Programs.


On Monday, the FDA announced that it sent warning letters to seven manufacturers of dietary supplements that contain the stimulant: Nutraclipse, Inc., Swagger Supps, Total Body Nutrition LLC, Xcel Sports Nutrition LLC, M4 Nutrition Companies LLC, Line One Nutrition Inc., and Chaotic Labz.

In each letter, the agency wrote that “methylsynephrine is not a vitamin, a mineral, an herb or other botanical, or an amino acid,” and does not otherwise meet the definition of a dietary supplement.

“Declaring methylsynephrine in your product labeling as a dietary ingredient causes your products marketed as dietary supplements to be misbranded … in that the labeling is false or misleading,” wrote William A. Correll, director of the Office of Compliance at the FDA’s Center for Food Safety and Applied Nutrition.

The letters stopped short of calling methylsynephrine a drug, although it is generally defined as a stimulant that mimics the effects on the heart of an amphetamine. The companies have 15 days to tell the FDA how they will bring their products into compliance with the law.

Dietary supplements include such ingredients as vitamins, minerals, herbs, amino acids, and enzymes. Unlike drugs, according to the FDA, supplements are not intended to treat, diagnose, prevent, or cure diseases, and, unlike drugs, should not make claims to do so.

Under a 1994 law, the FDA has been permitted to take products off the market, after establishing that they are unsafe or labeled in a way that is false or misleading.

But the law also loosened one critical rule. Dietary supplement makers were no longer required to get the FDA’s approval before selling their products — they only had to notify the agency that they planned to include a new ingredient in a product. It doesn’t always work that way.

“We have never received notification from any companies that wanted to market methylsynephrine,” said Tave. “Our contention is that methylsynephrine is not at all a dietary supplement under the statute. If we had gotten a notification, we would have responded and said it was not a dietary ingredient.”

An FDA spokeswoman said the agency had learned of 47 adverse reactions associated with the stimulant, which is available online and in stores that specialize in natural products.

Although the FDA reports problems people have had with drugs or medical devices, it does not do so for dietary supplements, an exemption criticized by Dr. Pieter Cohen, an assistant professor at Harvard Medical School and an expert on dietary supplements.

“It’s another way the industry is in control of the process,” Cohen said. “There’s no public health reason not to release it. The industry has been pushing against it.”

Cohen, who raised concerns about methylsynephrine with the FDA in January, said supplements containing the ingredient are linked to vomiting, agitation, and cardiac arrest. He said he was particularly concerned that users of methylsynephrine would likely not know how much of the drug they were getting in the supplements.

“There’s no law saying that the amount of each ingredient needs to be on the label,” Cohen said.

For their part, FDA officials say they don’t have the money or staff to chase the vast number of dietary supplement manufacturers, some of whom will make a product, receive a warning letter, shut down, and reopen under a new name.

But that defense doesn’t sit well with agency critics like Democratic Senator Claire McCaskill of Missouri, who for years has pushed the FDA to be more aggressive at policing dietary supplements.

“Today’s action can be filed squarely in the ‘better late than never’ category,” McCaskill wrote in an email to STAT. “For the past seven years athletes have been prohibited from using this substance, but the FDA waited until today to act. We have a system in which tainted and adulterated dietary supplements routinely make their way to consumers because Congress and the FDA refuse to take even the smallest steps to stop them, or as is the case with this substance, for the FDA to inform consumers of the existence of potentially dangerous ingredients.”