The caffeinated females weren't just looking for company. "It looks as if they wanted to have sex again," researcher Fay Guarraci, PhD, tells WebMD.
The study, titled "Coffee, Tea, and Me," is due to appear in an upcoming issue of Pharmacology, Biochemistry, and Behavior.
Consume Caffeine, Crave Sex?
Guarraci isn't advising women to use caffeine as an aphrodisiac -- at least, not yet.
"My caution in terms of directly applying the caffeine or the coffee before sex to enhance your sexual drive or motivation would be that in this experiment, we gave only one dose of caffeine to animals who had never had caffeine before," Guarraci says.
"Most of the time, women drink coffee on a daily basis or ingest caffeine in cola beverages," she observes.
It would be interesting to see if regular caffeine use had the same effect on female rats, Guarraci says. If she knew that to be true, she would "be more confident in saying that it would be something useful for women to consider," she says.
Still, she notes the current study's results "might be something to think about for women who don't ingest a lot of caffeine, who usually have a low level of caffeine in their diet."
Female Rats Returned for More Sex
The caffeinated female rats weren't exactly shy.
"The way we measure their interest is they go back and revisit the male after they've just had some sexual interaction with them," Guarraci explains.
That's a normal behavior for female rats. In this study, speed and motivation mattered.
The caffeinated females "would go and visit faster, and they would stay with the males until they received sexual stimulation before they left," Guarraci says.
"It wasn't just that they wanted to be around them. It seemed to be particularly relevant to the sexual interaction, the stimulation they would receive," Guarraci says.
Caffeine didn't affect how quickly the female rats left their partners after sex, the study shows.
A Large Latte's Dose of Caffeine
The researchers tested several caffeine doses on the rats. The doses were based on the rats' weight. Interestingly, the female rats that received the middle dose of caffeine had quicker return visits to the males than the highest dose tested.
Using the same formula for humans, the lowest dose would roughly equal the caffeine in "a grande latte at Starbucks ... a pretty high-caffeinated beverage, but not something outrageous," Guarraci says.
The higher doses were like having several large lattes at once, she says. Were the rats totally wired by the caffeine? "No," Guarraci says.
Her study shows that the caffeinated females didn't just skitter around their cages aimlessly. Instead, they specifically sought a male sex partner and weren't particularly interested in socializing with another female rat.
The caffeinated females seemed motivated to seek sex, not to burn extra energy from the caffeine, the researchers write.
Do You Mate Like a Rat?
Rats and humans are obviously different. But rats' elaborate courtship behavior may sound familiar to some people.
"The female seems to control the mating encounter," Guarraci says of rats.
"So when a male and a female rat are ready to mate, the female does all the gatekeeping for the male. She decides when it's time for him to mate, in the wild as well as in the lab," Guarraci says.
"The female, when she's interested, she'll go visit a male. But then when she's not interested in him anymore or wants to take a break, she runs away. To me, it seems a little bit like the playing hard-to-get with the male rats," she continues.
Ultimately, Guarraci and colleagues want to identify the chemistry and brain structures involved in sexual motivation for mammals, which include people, as well as rats.
"There are a lot of women out there with sexual dysfunction, and if they understood how that happens or how we can augment that, that would be a helpful thing," Guarraci says.