Warning: 'Natural' sex supplements may not be

(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.

One Dutch study found that about three-quarters of the products sold in the Netherlands contained at least one analogue, while the U.S. Food and Drug Administration recently discovered three analogue drugs (as well as counterfeit Viagra) when it analyzed a product called Mojo Nights. Other tainted supplements include those sold under the names Vicerex, Bullet Proof and Lightning ROD.

Analogues are particularly troublesome, says Cohen, because they have never been tested in humans, so their potential side effects remain a mystery.

Read more:
Warning: 'Natural' sex supplements may not be