Why do men need a "recovery period" after orgasm? And why is sexual intercourse more satisfying than masturbation alone? Now scientists think the two phenomena might be linked.

Making abstraction of psychological arguments, scientists looked for the chemical substances released after orgasm. In order to do such a thing they turned to volunteers who agreed to masturbate or to have sexual intercourse in the lab.

Stuart Brody of the University of Paisley, UK, and Tillmann Krüger of the Swiss Federal Institute of Technology in Zurich, measured blood prolactin levels in male and female volunteers after orgasm. Prolactin is a hormone released after orgasm into the bloodstream in both men and women. This hormone counteracts the effects of another hormone, called dopamine, which is released during sexual arousal.

What scientists found was that, after orgasm from sexual intercourse, the increase in blood prolactin levels is 4 times higher in both sexes compared with the levels after orgasm from masturbation.

According to Brody, this explains why orgasm from intercourse is more satisfying than masturbation. This discovery also explains why men experience a "recovery period" because elevated levels of prolactin have been previously linked to erectile dysfunction. So, the increase of this hormone, needed to counteract the escalating levels of dopamine, produces the "recovery period".