Mar. 29 -- FRIDAY, March 28 (HealthDay News) -- A combination of testosterone and progestin suppresses sperm production faster and more completely than testosterone alone, according to an analysis by an international team of researchers.
The scientists said that hormonal contraception may become a safe, effective and reversible form of male birth control.
"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," lead author Peter Y. Liu, an associate professor at the University of Sydney, Australia, said in a prepared statement.
Testosterone and other male hormones create "negative feedback" in the male reproductive system, which suppresses sperm production.
In this study, Liu and colleagues analyzed 30 male hormonal contraceptive studies that included a total of 1,756 men, aged 18 to 51. In these studies, conducted from 1990 to 2006, the men received different preparations of testosterone, with or without various preparations of the hormone progestin.
Testosterone is the primary male sex hormone. Progestin (a synthetic progesterone), which is used in combination with estrogen for female contraception, is not ordinarily produced by men.
The analysis revealed that the combination of testosterone and progestin was more effective at suppressing sperm production that testosterone alone.
"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," Liu said.
The analysis also showed that treatment suppressed sperm output more quickly in white males but not as completely as in non-whites. Younger men with lower testosterone levels also had faster sperm production suppression.
The review authors also found that it's difficult to predict which men will respond best to this combination hormonal contraception.
"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," Liu said.
The study was published in the Journal of Clinical Endocrinology & Metabolism.
The American Academy of Family Physicians has more about birth control.
SOURCE: Endocrine Society, news release, March 25, 2008