Scientists say they may have discovered why some women who use birth control pills suffer long-term sexual dysfunction — low levels of unbound testosterone.

A study of 124 women with sexual problems lasting more than six months showed they had reduced levels of unbound testosterone, the BBC reported.

Long-term exposure to the estrogens in the pill may lead to gene imprinting that results in over-production of the protein called sex hormone binding globulin, the researchers said. The protein binds testosterone, rendering it unavailable to the body.

Researchers said the high level of the protein persisted in women who had stopped taking it.

This study is a revelation, said Andre Guay, co-author of the study published in the Journal of Sexual Medicine and director of the Center for Sexual Function in Peabody, Mass. For years we have known that a subset of women using oral contraceptives suffer from decreased sex drive. We know that the pill suppresses ovulation and the male hormone (through production of SHBG). Therefore these pills decrease a woman’s male hormone availability by two separate mechanisms. No wonder so many women have had symptoms.

More here.