A woman in Sweden had a stroke while exercising, and doctors suspect it was caused by an ingredient in a workout supplement that she was taking — a compound similar to amphetamine.

The 53-year old woman, who was previously healthy and physically active, took a single dose of a sports supplement called Jacked Power (manufactured by the Swedish company MM Sports) shortly before she started her usual, vigorous workout in January 2014.

About 45 minutes into her workout, she started feeling numbness and clumsiness in her left hand, which continued for the rest of the day, and so she went to her doctor. A CT scan showed she had experienced a hemorrhagic stroke, a type of stroke in which a blood vessel bursts or leaks blood into the brain. She recovered, and was discharged from the hospital after five days.

But the woman didn't have any risk factors for stroke — she had a normal blood pressure and weight, and no one in her family had experienced a stroke. Doctors in Sweden concluded that it was likely something in the supplement she took that led to her stroke, and they published a report about her case last year.

As Livescience.com reports, after hearing of the case, doctors in the United States asked to test a sample of the woman's supplement for drugs that were not listed among the ingredients on the label, but could have caused the stroke. The only drug found in the supplement was a compound called beta-methylphenethylamine (BMPEA), which is chemically similar to amphetamine, but has never been tested in people, so its health effects are unknown, according to the report published online today (May 11) in the journal Annals of Internal Medicine.

"This is the first time that we have been able to clearly link BMPEA supplement use with a very serious health consequence," said Dr. Pieter Cohen, a co-author of the report and an assistant professor of medicine at Harvard Medical School.

In recent years, BMPEA gained increased attention after researchers found the drug in a number of dietary supplements marketed for weight loss and improved athletic performance. In April, the Food and Drug Administration warned five companies to remove the compound from their products, saying that BMPEA did not meet the criteria for a dietary ingredient.

Although the FDA stopped short of saying that BPMEA could be harmful, doctors have been worried that the drug could pose health risks. The new report now provides more evidence of the compound's potentially harmful effects, in that the combination of BMPEA and exercise "appears to be the most probable cause of her stroke," Cohen said.

Studies of BMPEA done in animals in the 1930s and 1940s found that the compound increased heart rate and blood pressure in cats and dogs, although exactly how BMPEA affects the human body isn't known.

Exercise in general increases blood pressure, and so "if the BMPEA further increased blood pressure, that could pose a risk of a bleeding stroke," Cohen said.

Still, the researchers cannot definitely say that the woman's stroke was caused by BMPEA. In rare cases, seemingly healthy people can experience a stroke while exercising. But in these cases, people typically have an underlying brain aneurysm, or a weakening of the blood vessels in the brain that can increase the risk for a hemorrhage.