I've been reading the book "How We Do It: How the Science of Sex Can Make You a Better Lover" by Judy Dutton. [Note- if you're interested, used copies are available for a Bareefoot Running Book-esque price of $0.01 via Amazon] The book discusses a wide variety of fascinating sexuality topics derived from research. It's an infinitely better basis for sexual knowledge than that bullshit published in puppy cage liners like Cosmo, Redbook, and Men's Health. I highly recommend the book based on what I've read thus far.
One of the first studies the author discusses is a correlational study by Gallup, Burch and Platek (2002) that discusses a positive correlation between condom use and depression. The authors of the study hypothesize the cause of the correlation could be due to prostaglandins present in semen that are absorbed into the recipient's body which wards off depressive symptoms.
I'll take a moment to let all the dudes rejoice.
If you think this is the greatest idea ever stop reading here. Print out the Gallop et. al. abstract and tactfully give it to your significant other... preferably when they're in a bad mood. Offer up a nice "deposit" for... you know, humanitarian reasons. Better yet, all the guys can now add "Bringer of Happiness" to their resumes or CVs.
If you're more of a research geek, read on.
Like all sexuality research, it's a good idea to read the fine print. The Gallup study was correlational in nature, which means the results can't say if the lack of condoms (and accompanying creampie) caused the decrease in depression. The authors of the study did control for a variety of extraneous variables, which does increase the validity. Still, causation can't be established with correlational research.
Psychology Today posted a nice critical article, which is worth a read. The PT article does note Gallup et. al. have replicated the results with a larger sample size, but the same correational issues will still be an issue.
Could causation be tested?
It would be somewhat difficult in the lab, though I could imagine groups of subjects ingesting caplets filled with either semen or a placebo.
It would be much easier to test this hypothesis at home. After all there's nothing more reliable and valid than the n=1 experiment. This home experiment requires a "donor" and a "recipient." If you're in a relationship without a donor, you're fucked. And resigned to spend a lot of time being angry. ;-)
Bad jokes aside, the experiment s very simple. Have sex (vaginal oral or anal... all are acceptable methods to absorb the hormones in the semen.) About half of the time the donor will finish up inside the recipient. For the other half, the donor will finish up outside (note- some believe semen also has positive effects on skin health.) Otherwise they to keep every other variable the same. If the recipient normally orgasms as part of the sexual acts make sure they continue in both conditions.
Record the mood of the recipient in the hours after the experiment. After a few weeks, you should see a pattern developing if one exists. If there is a pattern, congratulation! You've stumbled upon an easy route to happiness! If there is no pattern, at least you've had a lot of sex.
It's a win-win!