"Man Up Now" sounds like a pretty strong name for an "all natural" and "herbal" male enhancement product. But the FDA slammed those claims, warning consumers to "stop using them immediately."

The issue, says the agency, is the product uses "sulfoaildenafil, a chemical similar to sildenafil, the active ingredient in Viagra."

Like Viagra, sulfoaildenafil can have dangerous interactions with other prescription drugs such as nitrates, and can cause dangerously low blood pressure. But because consumers think they are taking a "natural" product they are usually not under a doctor's care.

Also, sulfoaildenafil has not undergone the same clinical trials as sildenafil, so all its effects are not known.

FDA Warning

It's not clear if "Stiff Nights" is a "dietary supplement" as its maker claims, or a bad b-movie title, but in either case the FDA says men looking to "regain the thunder" should stay clear because the pill really contains sulfoaildenafil, an untested chemical similar to the active ingredient in Viagra, which can interact badly with nitrates and cause low blood pressure.

FDA Warning.

The marketing geniuses behind "Stiff Nights" also sell "Rock Hard Weekend." Same unregulated chemical, says the FDA, different laugh out loud brand.

FDA Warning.

It's not clear who Don Wands is or how he became so magical, but the FDA didn't seem to care.

In August 2010, they told the manufacturer of this supplement to drop the magic act and take it off the shelves because the product's two main ingredients, hydroxyhomosildenafil and sulfoaildenafil, aren't listed on the box, aren't "supplements" and aren't really tested.

FDA Warning.

It's not magic in this instant coffee sold to boost sexual performance. The FDA says the secret sauce in the "100% natural" products is actually hydroxythiohomosildenafil , a chemical very similar to Viagra which can interact badly with nitrates and cause low blood pressure.

Magic Power Coffee's website says the extra mojo comes from honey goat weed and goji berries.

FDA Warning.

If you wind up with Duro Extend in your stocking this year, you might want to send it back to Santa.

The FDA recalled the product in early December 2010 because the "dietary supplement" is secretly supplemented with sulfoaidenafil, a drug similar to Viagra, but not tested.

FDA Warning.

Vigor-25 may be keeping hope alive for its users, but the FDA says the product marketed as a "natural dietary supplement to enhance male sexual performance," is really giving consumers a dose of sulfoaildenafil, a chemical similar to sildenafil, the active ingredient in Viagra.

"This product is dangerous to consumers because it claims to contain only natural ingredients when it actually contains a prescription drug ingredient," says the FDA's warning letter.

Dangerous interactions with nitrates and low blood pressure are possible.

FDA Warning.

The FDA is giving "Time Out" capsules a real time out. The agency says the product marketed as "100%" natural is really just a Viagra rip off in disguise. The agency says the pills contain "hydroxythiohomosildenafil, a chemical similar to sildenafil, the active ingredient in Viagra. Like sildenafil, this chemical may interact with prescription drugs such as nitrates, including nitroglycerin, and cause dangerously low blood pressure."

FDA Warning.

If patients want Viagra, they visit a doctor. If they want more Vitalex, they might consider a trip to a federal prison in Texas, where company founder Phu Tan Luong is serving a 10-year sentence for an unrelated Medicare fraud.

The FDA doesn't recommend hitting up Luong for pills, however. They say Vitalex's "all natural" and "herbal" concoction is really acetildenafil, another chemical similar to the drug in Viagra, but not tested.

FDA Warning.

Eager men trying to get their hands on a box of Xiadafil VIP, might have to wait in line. In July 2010, U.S. Marshals seized almost $75,000 worth of it after the manufacturer refused an FDA request to recall it.

The problem? The FDA says the product's VIP power comes from hydroxyhomosildenafil, a drug similar to Viagra, but untested.

FDA Warning.