The trouble with the pill is that what keeps you from getting pregnant -- stopping ovulation -- is also what can sap your sex drive. Your ovaries make hormones as well as eggs, and when they're put to rest for several weeks each month, hormone levels in your body drop. The second problem is that the pill causes the body to produce a protein called sex hormone binding globulin (SHBG), which binds itself to sex hormones, in particular testosterone, essentially sucking them up. Testosterone plays a role in vaginal blood flow and sensitivity in the opening of the vagina, so lower levels of this hormone can lead to sexual problems. What's more, the thinking was that once you stopped the pill your body returned to its original settings, but research shows the pill's effect and the SHBG protein production can continue to be higher in former pill users than in non-pill users.