It's widely assumed that this increase in risk is because alcohol has biologically disinhibiting qualities that make taking sexual and other risks more acceptable, but is that true? Will alcohol always increase the odds that a couple will practice unsafe sex? Or is combining drinking and sex risky for a different reason entirely?
There are several possible ways that alcohol might increase sexual risk taking. It might make people less likely to talk before having sex, make it harder to remember to use condoms or use them correctly, increase the likelihood that someone would choose a risky partner, or make it more likely for someone to do things (or sleep with people) they wouldn't consider when sober.
There is data, in fact, that alcohol can do all these things, but the reasons may not be precisely what you expect. Several studies have suggested that alcohol isn't naturally disinhibiting, at least not to the extent it seems to be in American society. Instead, the reason alcohol use is associated with sexual risk taking is that people expect it to be.
People who believe that alcohol is disinhibiting -- that it encourages sexual risk taking, violence, or other behaviors that people avoid when sober -- are more likely to be disinhibited by alcohol than people who have no such expectations. Interestingly, several studies have found that an increase in sexual risk taking while drunk is particularly problematic with casual partners (people who aren't in a long term relationship but aren't having sex for the first time), when compared to new sexual partners or regular sexual partners. This may be because people are trained to be cautious with new partners, and condoms may be habitual with regular partners, but with casual partners no pattern has been established.
What's the take home message? Alcohol may increase sexual risk taking, but it doesn't have to. It's possible to combine drinking and sex in a relatively safe manner if you believe that you can. Therefore, alcohol use is no excuse for indulging in risky behavior -- sexual or otherwise. The things you do when you're drunk are your responsibility -- as is the fact that you chose to get drunk in the first place.
One final note: The 2005 study that looked at the risks of drinking and sex also discovered something disturbing about how college men think about their relationships. Although monogamy is generally thought to be associated with a reduced risk of STDs, almost every young man in the study stated that they were in monogamous relationships even when they had multiple partners within a period of a few days to a few weeks.
This type of serial monogamy, where a person is only having sex with one person at a time but quickly moves from one partner to the next, is not the sort of low-risk, mutually-monogamous relationship that most educators are referring to when they praise the benefits of monogamy. Instead, the false assumption of safety may actually make serial monogamy a higher risk lifestyle than having multiple concurrent partners -- where the level of danger must be acknowledged so that safe-sex becomes a priority.
"Alcohol use, partner type, and risky sexual behavior among college students: Findings from an event-level study." Brown JL, Vanable PA. Addict Behav. 2007 Dec;32(12):2940-52. Epub 2007 Jun 9.
"Effects of alcohol, expectancies, and partner type on condom use in college males: event-level analyses." LaBrie J, Earleywine M, Schiffman J, Pedersen E, Marriot C. J Sex Res. 2005 Aug;42(3):259-66.