Five years ago, a team at Georgia State University discovered that people who are involuntarily celibate or abstinent and often exhibit depressive feelings (like anger, frustration, self-doubt, and even proper depression) are driven into this by "missed opportunities", due to living without sex.

Another researcher disagrees with this and says that it may not be the sex per se, but lack of semen exposure.

"Semen appears to act as an antidepressant in women," said psychologist Dr. Gordon Gallup of the State University of New York in Albany.

"In our studies, women who have unprotected sex have lower levels of depression, as measured on the gold standard evaluation tool, than those who have the same amount of sex with a condom. In fact, we found no difference in depression scores between women having heterosexual sex with condoms, lesbian sex, or not having sex at all," added Gallup.

In another research made two years ago, women practicing sex without condoms were more likely to exhibit depressive signs once they experienced sexual halts than those who stopped an intense sexual active period but whose previous partners employed condoms.

"Women [who have sex] without condoms are also more likely to fall victim to the rebound effect following the breakup of their relationship. This suggests that there is a withdrawal effect that influences depressiveness when semen exposure stops," said Gallup.

Anyway, protected or not, sex and orgasm do provoke a release of endorphins, the "happiness" brain hormone that brings mood up and dull pain.

"But I'm not sure that's the sole explanation, because the effects of endorphins wear off in about an hour," says psychologist and sex therapist Dr. Robert Hatfield, of the University of Cincinnati and a spokesman for the Society for the Scientific Study of Sexuality, who believe touch from a spouse or other trusted lover can trigger hormonal boosts.

"We know that people who touch and are receptive to touch are more likely to be happy and have fewer problems with depression and anxiety. Especially in a committed relationship or marriage, sex provides more opportunity for touch. I think orgasm is Mother Nature's icing on the cake, a reason to make you want to go back for more the next time," said Hatfield.