A stimulant not approved for use in the U.S. has been found as an ingredient in 14 dietary supplements marketed as weight loss aids or pre-workout boosters, according to research published Thursday in the journal Drug Testing and Analysis.

A study led by Dr. Pieter Cohen, an internist at Cambridge Health Alliance and an assistant professor at Harvard Medical School, detected oxilofrine, also known as methylsynephrine, in 14 products, ranging from trace amounts to 1.5 times the adult pharmaceutical dose.

The research comes just days after the FDA sent warning letters to seven dietary supplement companies informing them that products listing methylsynephrine as an ingredient must comply with federal law, which prohibits dietary supplements from containing unapproved pharmaceutical drugs.

Oxilofrine is used in some countries to treat medical conditions such as low blood pressure and asthma, but it is not approved for use in the U.S.

The study tested 27 brands of dietary supplements that listed methylsynephrine or some variation of the name, such as methyl synephrlne or methyl-synephrine, as an ingredient and found that 14 contained the stimulant.

One supplement, Shredder by Total Body Nutrition, contained nearly twice the usual adult dose in one capsule and three times the usual adolescent dose, according to the study.

The authors said the "consumption of supplements containing oxilofrine may pose serious health risks" to consumers. "One brand of supplements containing oxilofrine has been linked to serious adverse events including vomiting, agitation and cardiac arrest," Cohen wrote.

Oxilofrine, which is banned by the World Anti-Doping Agency, is the same stimulant blamed for the downfall of several world-class athletes: In 2013, U.S. sprinter Tyson Gay and Jamaican runner Asafa Powell tested positive for oxilofrine and were subsequently banned from competition for more than a year.

Powell attributed his positive drug test to accidental ingestion of the substance from a contaminated dietary supplement.

The FDA has received 47 reports of adverse events associated with methylsynephrine, according to press officer Lyndsay Meyer. She noted, however, that a report only indicates that a patient developed symptoms and that the ingredient is not necessarily responsible.

According to the FDA, a dietary ingredient is "a vitamin; mineral; herb or other botanical; amino acid; dietary substance for use by man to supplement the diet by increasing the total dietary intake; or a concentrate, metabolite, constituent, extract, or combination of the preceding substances."

But in warning letters to the companies, officials noted that "methylsynephrine is not a dietary ingredient within the definition set forth."

"Methylsynephrine does not fit under any of these categories, rendering misbranded any dietary supplements that declare methylsynephrine as a dietary ingredient," according to the letters.

The FDA also told makers of one product, Lean Pills by Line One Nutrition, that it lists another illicit ingredient, methylhexanamine, as an ingredient in the product. According to the FDA, methylhexanamine is known by another name, dimethylamylamine, or DMAA, a banned substance.

Cohen said dietary supplements are allowed to contain botanical extracts and ingredients, and one popular ingredient, synephrine, made from bitter orange and other citrus species, is a legal supplement and shouldn't be confused with methylsynephrine.

Cohen and his team said the research has a few limitations, including that scientists tested only one sample per brand and looked only at products that claimed methylsynephrine as an ingredient.

"It is possible that other brands of supplements on sale in the USA may also contain oxilofrine without listing methylsynephrine on the label," they wrote.

American Metabolix, makers of Exile, a weight loss product named as one of the 14 containing oxilorfrine, sent a statement to Military Times saying the company has never used oxilofrine in supplements and that its products comply with the Dietary Supplement Health and Education Act "100 percent of the time."

"Stating that we use a 'drug,' the same one Olympic athletes were using to cheat (Tyson Gay) is 100 percent disingenuous," American Metabolix managers wrote in the statement.

Another supplement found to contain oxilorfrine, Miami Lean, by Skyline Nutrition, has been removed from the market, a company spokesman said.

"I followed FDA advice and discontinued Miami Lean," a Skyline Nutrition executive wrote in a Facebook message to Military Times.

Some of the products named, including Hi-Tech Pharmaceuticals' Fastin, Advanced Nutrition Systems' Methyl Drive 2.0, and American Muscle Sports' Exile, are or were sold at GNC, which has stores on many military installations.

Many of the products also are available online.

Patricia Kime covers military and veterans health care and medicine for the Military Times. She can be reached at pkime@militarytimes.com.

Patricia Kime is a senior writer covering military and veterans health care, medicine and personnel issues.

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