The tests sought to establish the exact contents of the Jacked Power product, which was linked to the cerebral haemorrhage of a healthy 53-year-old woman without risk factors for vascular disease.
The product was pinpointed as a potential cause in the original medical report at the end of last year, but beta-methylphenylethylamine (BMPEA) had not been detected at this point.
The product's ingredient list included β-phenylethylamine and its derivative N,N-dimethyl-phenylethylamine, substances structurally very similar to amphetamine. However, BMPEA was not listed.
Writing this month in Annals of Internal Medicine, the US and Swedish doctors said: "Exercise combined with BMPEA, an isomer of amphetamine, probably caused this patient’s stroke. Case reports are available of exercise-induced hemorrhagic stroke in otherwise healthy patients, and amphetamine has also been identified as a cause of hemorrhagic strokes in many case reports. However, the health effects of amphetamine’s β- isomer, BMPEA, are unknown."
The report came as the US Food and Drug Administration (FDA) issued warnings on the amphetamine substance and a separate report - which shared one of the same authors, Dr Pieter Cohens - found 11 out 21 supplements screened contained BMPEA. The maximum daily dose found in this earlier report was 93.7 mg, far below the amount found in Jacked Power.
BMPEA is classified as a banned substance according to the World Anti-Doping Agency (WADA). The FDA announced its ban as an ingredient in food and supplements last month.
Rickard Zeijlon, one of the Swedish doctors who treated the woman and author of the report, told us the Swedish National Food Agency (NFA) had been notified but so far no action seemed to have been taken.
The NFA did not respond to our request for comment in time for the publication of this article.
The FDA was also notified.
MM Sports responds
MM Sports, the online retailer behind the own brand product, said it had been voluntarily withdrawn from market due to a drop in popularity nine months before the "unfortunate incident".
A spokesperson told us the product had been on the market for a year and a half without any issues of this kind being reported.
"We are a bit surprised that they found BMPEA in the product, but the product contained a mixture of phenylethylamines which have similar structures and properties, which may have been mistaken for BMPEA in the analysis. BMPEA have been on the market for several years, both EU and US market, without any issues reported to our knowledge."
The doctors wrote that this was the "first identified case of a hemorrhagic stroke probably caused by exercise combined with BMPEA" to their knowledge.
Dr Zeijlon said the most worrying element of the findings was that the substance was an adulterant and therefore unlabelled. "So it's of course very alarming to find a large dose of a highly active synthetic stimulant that the consumer has no way of knowing is present."
Degree of certainty
MM Sports stressed that, like the original medical report of the stroke, the conclusion was not that the product was to blame for certain but that there may be a connection.
The paper categorised the causality as “probable/likely,” which the World Health Organisation’s (WHO) Adverse Reaction Terminology defined as: “A clinical event [...] with a reasonable time relation to administration of the drug, unlikely to be attributed to concurrent disease or other drugs or chemicals and which follows a clinically reasonable response on withdrawal."
The product was tested by the Netherlands’ National Institute for Public Health and the Environment (RIVM).