It is a statement on the evolution of society’s attitudes toward sex when you compare the concerns that were raised about the birth control pill 50 years ago – when it was approved by the Food and Drug Administration – with those of today.
In the 1960s, there was much hue and cry that the Pill would turn women into sex fiends and put marriages in peril. But in recent decades, medical concerns about hormonal birth control have shifted to the other end of the spectrum, with doctors maintaining that it may actually lower women’s libido and in some cases lead to sexual dysfunction.(Watch a TIME video on the Pill’s importance.)
Now a new study of female sexual function, published this week in the Journal of Sexual Medicine, adds evidence to the argument. Using questionnaires to assess sexual function in more than 1,000 female medical students in Germany, researchers found that women who used a hormonal method of birth control – mostly oral contraceptives – had lower levels of sexual desire and arousal than women who used nonhormonal methods like condoms or no contraception at all.
“To our knowledge, this is the largest study in which the effect of hormonal contraception on sexual function has been evaluated. We had a large and homogenous group, and our results lead us to believe that hormones may indeed influence sexual function,” says Alfred Mueck, who directs the Center of Women’s Health at the University Hospital of TÜbingen in Germany and is one of the study’s authors.(See TIME’s special report on the state of the American woman.)
Mueck says the analysis of the data showed that the association between lower libido and hormonal contraceptives was independent of other variables, such as stress or relationship status, that are commonly known to contribute to low sex drive. But the author cautions that at this point, the data show only an association, not a cause-and-effect relationship between the Pill and sexual dysfunction.
Figuring out whether hormonal contraception can directly dampen libido would involve further study to isolate the mechanism at work.
In theory, however, it makes biological sense, says Anita Clayton, a University of Virginia professor of psychiatry who treats female sexual dysfunction and recently helped lead a clinical trial on the drug flibanserin as a potential treatment. Hormonal contraception has been shown in women to lower the level of free and available testosterone circulating in the blood. And although the evidence is still uncertain, testosterone is believed to play a role in sex drive in women. Testosterone treatment has been shown to relieve a common form of female sexual dysfunction known as hypoactive sexual desire disorder. Clayton says she has similar anecdotal evidence of the connection between the Pill and low sex drive from her own patients.
Further, says Kim Wallen, an Emory University professor of psychology and neuroendocrinology, sex drive appears to ebb and flow in tandem with hormone levels during a woman’s normal menstrual cycle. During ovulation, for instance – when the level of hormones rises in order to prompt the ovary’s release of an egg – women are more apt to initiate sex. The Pill works by preventing ovulation, and women who take it experience less hormonal fluctuation throughout their menstrual cycle.
Wallen notes that a study published in the New England Journal of Medicine as early as 1978 showed that women who were taking the Pill had no such midcycle rise in sexual motivation. Since then, however, other studies directly evaluating whether the Pill is associated with female sexual dysfunction have had varying and inconclusive results.
Clayton notes another weakness of the study: it was observational. Rather than randomly assigning women to use various methods of hormonal and nonhormonal contraception, the study involved women who had already chosen their method of birth control for themselves.
A larger criticism of research like Mueck’s is that it mischaracterizes female sexual dysfunction in general. As drug companies race to find treatments for problems like low sexual desire, researchers hotly debate whether such conditions should be considered a medical disorder at all, or whether low desire is really just a relational issue.
Mueck says his team is conducting a larger study that may include enough participants to enable them to break down results by length of relationship and by the dosage of hormones in various types of contraception.
Whatever the conclusion, Wallen says women are long overdue for a serious look at this issue. “I find it pretty surprising that millions of women have been taking the Pill for decades without anyone ever investigating the possible side effects [on their sex lives],” Wallen says.