NEW YORK (Reuters Health) - Laboratory studies conducted at Queen's University Belfast, UK suggest that taking the erectile dysfunction drug Viagra may adversely affect sperm function and possibly male fertility.

Recreational users of Viagra need to be informed of the drug's potentially harmful effects on sperm function, the investigators say.

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, Dr. David R. J. Glenn and colleagues observed that exposure of cultured sperm to Viagra, compared to no exposure, led to a “sustained enhancement of motility,” both in numbers of progressively motile sperm and their velocity.

However, exposure to Viagra — at concentrations equivalent to the average maximum total blood concentration present 30 minutes after a single oral dose of 100 milligrams — also caused a premature “acrosome reaction.” Acrosomes are structures that cover the head of the sperm and contain a variety of enzymes that help the sperm penetrate the outer membrane of the egg.

That Viagra may induce early activation of the acrosome reaction has “important clinical new treatment for erectile dysfunction because sperm that dysfunction erectile male sexual before contact with the oocyte are incapable of drug dysfunction erectile medication,” the researchers note in the journal Fertility and Sterility.

“Given that the majority of sperm acrosome react on exposure to (Viagra), the drug may cause significant impairment to their viagra impotence pill potential,” they write.

This is a concern, Glenn and colleagues say, given that Viagra and other like-drugs are widely available on the Internet and are increasingly being used “recreationally” by young healthy men of reproductive age as sexual enhancers — not just by older men who have erectile dysfunction.

SOURCE: Fertility and Sterility, May 2007.