Warning: Men's natural sex supplements may not be

Sexual supplements marketed to men can be dangerous and may contain variants of prescription drugs, a new report finds.

STORY HIGHLIGHTS

Editor's note: Ian Kerner, a sexuality counselor and New York Times best-selling author, writes about sex and relationships for CNN Health. Read more from him on his website, GoodInBed.

(CNN) -- Conventional wisdom tells us that natural remedies are simply gentler alternatives to prescription drugs like Viagra and Cialis, right?

Not so fast, say experts. Not only are many dietary supplements marketed for erectile dysfunction and other male sexual problems ineffective, they may not even be "natural."

In fact, a number of these supplements are adulterated with the very prescription drugs they claim to replace, according to a recent report published in a recent issue of JAMA Internal Medicine.

The editorial by Dr. Pieter Cohen, an assistant professor of medicine at Harvard Medical School, sheds light on this growing concern. Cohen cites several alarming incidents in which over-the-counter sexual enhancement supplements were found to contain other substances.

For example, one study in Singapore found that 77% of so-called natural sex supplements on the market contained undeclared pharmaceutical drugs, often in higher-than-recommended doses.

And in 2012, a supplement called Rock Hard for Men was found to contain both counterfeit Cialis and glyburide, a diabetes drug. A similar combination found in other sex supplements has been tied to the deaths of more than a dozen men in Asia.

Even more disturbing, such supplements may contain analogues, or chemical variants, of prescription drugs like Viagra. Indeed, more than 45 new analogues have been identified in sexual supplements, according to Cohen.

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Warning: Men's natural sex supplements may not be