In a world where women take more control of their lives, men get more involved in the contraception process. That's why the male pill may not be such a weird issue soon. Hormonal contraception could be a safer, more effective and reversible method of male birth control compared to other methods (like vasectomy, for example). A new meta-analysis published in the "Journal of Clinical Endocrinology & Metabolism" points toward the best formula for such a medicine: a combination of testosterone and progestin, which proved to be better and faster than testosterone taken alone.

"It is possible to suppress sperm output to concentrations that are comparable with reliable contraception in most, but not all men. The rate of suppression is comparable to that achieved after a vasectomy," said lead author Peter Y. Liu, an associate professor at the University of Sydney, Australia.

Testosterone and other male hormones induce a "negative feedback" in testicles, translated through inhibited sperm production. The Australian team used data coming from 30 male hormonal contraceptive researches made on 1,756 men, aged 18 to 51. The studies were made between 1990 to 2006, and the subjects received various formulas of testosterone, with or without progestin.

Testosterone is the main male sex hormone, while progestin is a synthetic chemical similar to progesterone, a main female sex hormone, which in combination with estrogen makes the female contraceptive pills. The male body does not normally produce progesterone.

"Progestin co-administered with testosterone increased both the rate and extent of suppression. It also may make long-term hormonal contraception safer by reducing the dose of testosterone needed for maintenance contraception," said Liu.

The meta-analysis also pointed that the combination inhibited sperm production more rapidly in white males, but the suppression was more complete in non-white men. Younger men with lower testosterone amounts were also more sensitive to this hormonal combination.

"Considerable progress has been made toward finding an effective combination of these two hormones. However, the current analysis didn't take into account the different types of progestins, so more research will need to be done to find the optimum therapy," said Liu.