A product called Magic Power Coffee, marketed for sexual enhancement, contains an ingredient that could lower blood pressure and should be avoided, according to the U.S. Food and Drug Administration.

Samples purchased and analyzed by the FDA found the product contains hydroxythiohomosildenafil, a chemical similar to the active ingredient in Pfizer's blockbuster erectile dysfunction drug Viagra.

'Consumers may assume it is harmless and poses no health risk ... in fact, Magic Power Coffee can cause serious harm.'—Deborah Autor, U.S. Food and Drug Administration

Like Viagra, Magic Power Coffee can interact with other drugs and cause dangerously low blood pressure. That can cause the brain to be deprived of an adequate blood supply.

"Because the product is an instant coffee labelled as an 'all natural dietary supplement,' consumers may assume it is harmless and poses no health risk," said Deborah Autor, the director of the FDA's Center for Drug Evaluation and Research, Office of Compliance.

"In fact, Magic Power Coffee can cause serious harm," she said.

Magic Power Coffee is sold on the internet and through multilevel marketing schemes. It sells for $6 to $8 per dose.

Horny goat weed claimed as active ingredient

According to the online Magic Power Coffee Club, the active ingredients are epimedium herb (also known as horny goat weed), goji berry and ginseng.

The only known study on horny goat weed was done by the departments of pharmacy and veterinary medicine at the University of Bologna in Italy in 2008. The research did not involve any human trials, but found that epimedium did contain a compound similar to Viagra.

'It is virtually impossible to predict possible risks' —Joe Schwarcz, McGill University

Joe Schwarcz of the office for science and society at McGill University in Montreal warns that "You never really know what you're getting," when it comes to commercial preparations using goat weed.

"Not knowing the exact composition of such products, it is virtually impossible to predict possible risks," Schwarcz wrote in an article on horny goat weed.

In its warning, the FDA says consumers shouldn't be taking chances. "Consumers who have Magic Power Coffee should stop using it immediately," states the FDA's warning.