Monday, November 29, 2010
It’s no secret that women who take a hormonal birth control pill have less interest in sex. One theory as to why is that combination birth control pills — which contain a synthetic form of estrogen and progestin — lower the levels of circulating testosterone in the body, thus lowering women’s libidos. But a new study published in the December issue of the American Journal of Obstetrics & Gynecology suggests that the makeup of the Pill may not be the culprit after all.
Researchers from Ohio State University College of Medicine tested 50 sexually active women who used either a combined oral contraceptive or a progestin-only injection. The combination birth control pill is thought to dampen libido in part by increasing the production of sex hormone binding globulin in the liver, a protein that binds to and inactivates circulating testosterone in the blood. In contrast, progestin-only injections, which lack estrogen, are thought to avoid this effect. (More on Time.com: 5 Little-Known Truths About American Sex Lives)
The women filled out a Female Sexual Function Index (FSFI), a questionnaire designed to measure sexual desire and satisfaction. They also had their testosterone and estrogen levels checked.
Although free testosterone levels were significantly higher among the women using the injection, there was no significant difference between the two groups’ scores on sexual desire or satisfaction. The women’s scores on the FSFI indicated high levels of sexual function, but the study did not compare their scores to those of a control group of women who did not use hormonal birth control. (More on Time.com: ACLU Cites Walgreens For Refusing Emergency Contraception to Men)