The US Food and Drug Administration has issued a warning to consumers, asking them to stop taking a product called Man Up Now capsules.
The FDA said that an analysis of Man Up Now showed that it contained sulfoaildenafil -- a chemical similar to sildenafil, the active ingredient in Viagra. This chemical could cause dangerously low blood pressure, the FDA warned.
"To date, the FDA is not aware of any adverse events associated with the use of the product," the FDA said in a statement. "However, sexual enhancement products that claim to work as well as prescription products, but that contain prescription strength drugs, are likely to expose unknowing consumers to unpredictable risks and the potential for injury or death."
The agency also said that while these products are claimed to be herbal, they did contain prescription drugs and could cause harm to consumers.