The U.S. Food and Drug Administration is warning consumers not to purchase or use Happy Passengers, a product promoted as all natural and sold for sexual enhancement and sold online and in some retail stores.

A FDA laboratory analysis confirmed the supplement contains a hidden drug ingredient called sildenafil, which is the active ingredient in the FDA approved prescription drug Viagra, used to treat erectile dysfunction, according to a public notification issued Jan. 21 by the FDA.

“This undeclared ingredient may interact with nitrates found in some prescription drugs such as nitroglycerin and may lower blood pressure to dangerous levels,” the FDA said.