The US Food and Drug Administration (FDA) has issued a heads up to men everywhere: Think really, really hard before taking any “dietary supplement” advertised to treat erectile dysfunction or enhance sexual performance in any way.

"The number of these problematic products available on the Internet appears to be increasing," says Michael Levy, director of the FDA's Division of New Drugs and Labeling Compliance. The division is part of the Office of Compliance (OOC) in the agency's Center for Drug Evaluation and Research (CDER).

The problem is that many of the products are being misleadingly advertised as “natural” or “herbal” alternatives to prescription drugs that have been approved by FDA. In reality, these products may be laced with potentially hazardous ingredients that have not been noted on the label.

How bad is it? In one FDA-led internet survey, more than one-third of"dietary supplements" claiming to spur sexual enhancement or treat ED contained undisclosed prescription drug ingredients or similar substances.

Beyond just “truth in advertising,” the big problem lurks in the dangerous ways the hidden drugs in your ED “supplement” could interact with other meds your are taking.

For example, sildenafil, a popular ED supplement, may lower blood pressure to an unsafe level when combined with certain prescription drugs containing nitrates.

“People with diabetes, high blood pressure, high cholesterol, or heart disease are often prescribed drugs containing nitrates, and men with these conditions commonly suffer from ED,” says Mark Hirsch, a medical team Leader in CDER's Division of Reproductive and Urologic Products. "Those are factors that doctors consider when prescribing approved ED treatments."

You would think the FDA would be in a position to shut the offending pharma makers down, but you would be wrong. Many of these products or their active ingredients are imported into the United States from other countries.

"FDA is working closely with US Customs and Border Protection to develop a more effective network to successfully screen and stop these shipments from entering US commerce," says Huascar Batista, team leader of OOC's Import-Export Team.

The FDA has published a list of products containing potentially harmful, undeclared ingredients. These include:

• Actra-Rx
• Actra-Sx
• Libidus
• Nasutra
• Neophase
• Vigor-25
• Yilishen
• Zimaxx
• 4EVERON
• Liviro3
• Lycium Barbarum L.
• Adam Free
• Rhino V Max
• V.Max
• True Man
• Energy Max
• HS Joy of Love
• NaturalUp
• Blue Steel
• Erextra
• Super Shangai
• Strong Testis
• Shangai Ultra
• Shangai Ultra X
• Lady Shangai
• Shangai Regular, also marketed as Shangai Chaojimengnan
• Hero
• Naturalë Super Plus
• Xiadafil VIP tablets (Lots 6K029 and 6K209-SEI only)

Sources: US Food and Drug Administration