The US drug safety watchdog warned consumers on Friday not to use a male sexual stimulant that is marketed as natural but contains the active ingredient found in Viagra.

The (FDA) said Vigor-25, which is sold as a natural dietary supplement to enhance male sexual performance, contains sildenafil, the active ingredient in , which could dangerously lower if it interacts with other prescription drugs.

The FDA is investigating the reported death of a 26-year-old man, possibly associated with the use of Vigor-25, the agency said.

Vigor-25 is distributed by Piston Corporation and is sold mainly on the Internet, although it could also be available through some retail outlets, the FDA said.