Male sex drive depends on estrogen, which is the main sex hormone in women, plays a bigger role in male libido than previously thought, according to research that may guide development of sex-drive treatments.

Besides testosterone, the male sex drive could very well depend on estrogen. Reducing estrogen in men undergoing treatment for low testosterone resulted in a drop in libido and an increase in body fat, even as testosterone levels improved, according to Bloomberg.

The testosterone caused men to have stronger sex drives than women, said Joel Finkelstein, a study author and endocrinologist at Massachusetts General Hospital, which was published in New England Journal of Medicine.

"What will surprise many people is that loss of sexual desire in men with low testosterone is due to lack of estrogen," Finkelstein said. "People think estrogen in men makes them very effeminate; they think of it as a female hormone, they think it is testosterone that gives men their sexual desire."

Mice were used for the research in this study. There also have been anecdotal reports of men undergoing sex changes who see an increase in libido when they start estrogen therapy. In women, it may be the opposite, where testosterone plays a bigger role than estrogen in their sex drive, according to Bloomberg.

Estrogens are a group of compounds named for their importance in both menstrual and estrous reproductive cycles. They are the primary female sex hormones. Estrogens are used as part of some oral contraceptives, in estrogen replacement therapy for postmenopausal women, and in hormone replacement therapy for trans women.

Functions of Estrogen:

Structural

Promote formation of female secondary sex characteristics

Accelerate metabolism

Increase fat stores

Stimulate endometrial growth

Increase uterine growth

Increase vaginal lubrication

Thicken the vaginal wall

Maintenance of vessel and skin

Reduce bone resorption, increase bone formation