Oh, come on…you know it's all about love in the case of Hugh Hefner and his herd of sexy blond bimbos. That's for sure, as an American research has showed that impotence drugs like Viagra act in more ways than producing an erection: they also boost the levels of the "love hormone".

The team at the University of Wisconsin-Madison reported in the Journal of Physiology that rats on Viagra (sildenafil) presented higher amounts of the hormone oxytocin. The hormone was initially involved in nursing and childbirth, and it is also linked to orgasm and sexual pleasure.

"It appears that Viagra and related drugs act on the part of the brain that controls release of oxytocin. This is one piece in a puzzle in which many pieces are still not available. But it raises the possibility that erectile dysfunction drugs could be doing more than just affecting erectile dysfunction," said lead researcher Meyer Jackson, a physiology professor at U W-M.

Viagra is an inhibitor of an enzyme called phosphodiesterase type five (PDE 5). Viagra and related impotence drugs, Cialis (tadalafil) and Levitra (vardenafil), employ the same mechanism to induce and maintain an erection. They inactivate the PDE5 enzyme that breaks down cyclic GMP. The result is an increase in the blood flow in the whole body, from penis to the brain, including a brain nucleus called the posterior pituitary, which naturally releases oxytocin, a phenomenon boosted by the increased blood flow, at least in rats.

"It probably does the same thing in people. It does the same thing it does in smooth muscle (of the blood vessels, which have to relax for increasing blood vessel diameter in the penis during the erection). Instead of (levels) coming down in a minute or two, they stay up a little longer," said Jackson.

Oxytocin's function for stimulating the milk production for breastfeeding was long known; more recently, it was discovered to be involved in human sexual arousal and function. "This could suggest other uses for Viagra and related drugs perhaps promoting social bonding. I hope that this doesn't cause some wild orgy of inappropriate recreational use", said Jackson.

Still, using the "love pills" for fun, instead of medicines prescribed to treat impotence, can have deadly side effects if mixed with some other drugs, and recent researches point to the fact that these pills could affect (in most cases permanently) the men's vision and hearing.