Pills marketed as safe herbal alternatives to prescription sex medication such as Viagra are not as innocuous as consumers may think, an investigation conducted by the Associated Press found.

Impotency products heralded as “all-natural” and bearing labels abundant in herbal ingredients also include unregulated versions of precisely the chemicals they are supposed to replace, the Associated Press reports.

These chemicals clash with nitrates millions of men around the world take in prescribed drugs for high blood pressure and heart disease, and often lead to a heart attack or stroke.

The AP says that its investigation emphasizes a growing public health concern that officials do not yet know how to track or ameliorate. This could prove difficult, as herbal impotency pills are much sought after – as sales worth approximately $400 million in 2006 prove.

At greatest risk are men who take nitrates and are well aware that prescription sex medication like Viagra, Cialis or Levitra is not recommended for them, should they wish to enhance their sexual performance.

James Neal-Kababick, director of Oregon-based Flora Research Laboratories, told the AP that about 90 percent of the hundreds of samples he has analyzed contained forms of patented pharmaceuticals. Some of these presented doses more than twice that of prescription erectile dysfunction medicine.

No deaths have been reported, yet all-natural sex pills have caused numerous emergency room visits, the AP notes.

Older men, more likely to have heart or blood pressure problems as well as erectile dysfunctions, are not the only ones that suffer unanticipated side effects of herbal pills.

The wire service reports that records of emergency room visits showed men in their 30s, in good health, nevertheless suffered after taking herbal sex pills, presenting side effects of the active ingredients in regulated impotency pharmaceuticals, such as difficulty seeing clearly or severe headaches.

Public health officials consider that these cases could be vastly underreported, with patients too embarrassed to share such experiences.

Sales of supplements marketed as natural sexual enhancers have been riding a good wave over the past years, rising $100 million since 2001, to an astounding $398 million last year, including herbal mixtures, according to estimates by Nutrition Business Journal, the AP reports.

Some encouragement comes from the fact that not all sellers advertising “magical” sexual enhancement are roaming freely on the Internet, where most “herbal” pills are sold. According to the AP, the U. S. Food and Drug Administration has been instrumental in eight recalls over the past year. The recalled products contained ingredients found in Viagra, Cialis or Levitra.