Despite the demise of Four Loko, vodka-Red Bulls and Jagerbombs remain popular on college campuses. Research has shown that mixing caffeine and alcohol makes people more likely to drive drunk or take other ill-advised risks. So addiction researcher Kathleen Miller asked college students on their drinking and sexual behaviors, and found that caffeine and alcohol may be more dangerous in this regard than alcohol alone.
For a study published in the Journal of Caffeine Research, Miller surveyed 648 students at the University of Buffalo, the majority of whom were between 18 and 21. She asked them how many times in the past thirty days they'd had alcohol mixed with an energy drink, and whether their most recent sexual encounter had been with a casual partner, been unprotected, or taken place while they were drunk or high.
While students who had combined caffeine and alcohol (about a third of the sample) were no more likely than others to have had unprotected sex recently, they were more likely to say their last partner had been casual — defined in the study as someone they weren't in love with, weren't exclusive with, and/or didn't know well. And they were more likely to have been drunk or high the last time they had sex. This was true for both men and women, and held even when Miller controlled for alcohol use generally — mixing drinks with caffeine appeared to have effects on sex that just plain alcohol didn't have.
Miller noted that the fact that energy drinks weren't associated with unprotected sex was one "hopeful" aspect of her study. However, she told BuzzFeed Shift, "consequences of hooking up drunk aren't limited just to unintended pregnancy or STDs; they can also include sexual victimization, post-sexual-encounter regret/shame, and social stigmatization ('slut shaming'), particularly for women." And, she added, "those risks are higher if you don't know your partner and his/her sexual history very well, and they're higher if you're drunk, because you're more likely to miss the often-subtle cues that tell you this encounter is a bad idea."
Though her study didn't address sexual assault, there's also some evidence that mixing alcohol and caffeine could make people both more vulnerable to assault and more likely to commit it. A 2007 study found that college students who drank the combinations "were more than twice as likely to take advantage of someone else sexually, and almost twice as likely to be taken advantage of sexually."
According to Miller, the reason alcohol and energy drinks together increase people's tendency toward risky behavior is pretty simple: "when you're drinking lots of alcohol, your judgment is impaired, and if you're having caffeine, you don't realize how impaired you are." Energy drinks remove the "cues" that you've had too much to drink — like feeling tired and lethargic — allowing you to drink more. There's also some evidence that energy drinks increase people's craving for more alcohol.
Banning the sale of Four Loko and other caffeinated alcoholic beverages is a step in the right direction, Miller writes in her paper, but it's far from a complete solution — college students are clearly capable of mixing alcohol and energy drinks themselves. She calls for better public education, so at least young people are aware that caffeine mixed with alcohol is likely to affect them more profoundly than booze alone.