Testosterone Tested as Male Contraceptive
Study Shows Monthly Injections in Men Can Prevent Partners' Pregnancies
May 6, 2009 -- After decades of delay, hormonal birth control for men may be a step closer to reality.
Monthly injections of a testosterone-based contraceptive were 99% effective for preventing partner pregnancy in what researchers say is the largest trial ever of a hormone-based male birth control approach.
Testosterone therapy is usually given to men to treat a condition resulting from a lack of testosterone. In men, testosterone controls sperm production, erections, and sex drive.
The study looked at fertile men, and treatment with testosterone was used to decrease sperm production. Testosterone treatment is known to decrease hormones of the brain that signal the testes to produce sperm.
Just over 1,000 Chinese men between the ages of 20 and 45 who had fathered at least one child within two years of enrollment took part in the study, which was published in The Journal of Clinical Endocrinology & Metabolism.
The search for a commercially viable male equivalent of the pill has been stalled in recent years, largely due to lack of interest by the pharmaceutical industry, says Elaine Lissner, who directs the Male Contraception Information Project.
"There has been a lot of consolidation within the industry, and several companies that were working on hormonal birth control for men abandoned development even though their studies were positive," she tells WebMD.
Companies lost interest, she says, because they concluded that there was not enough of a market for male birth control that required implants or frequent injections.
An oral male pill is not likely because testosterone is not as effective when taken by mouth and it can be toxic to the liver.
Studying Testosterone's Effects
The men in the Chinese study received monthly injections of a form of testosterone known as testosterone undecanoate (TU).
Lead researcher Yi-Gun Gu, MD, of Beijing's National Research Institute for Family Planning tells WebMD that while the contraceptive was found to be highly effective in the study, TU alone is not likely to be used in non-Asian populations.
Asian men seem to respond well to testosterone as a form of contraception, while studies in white men have shown it to be much less effective.
The reasons for this are not clear, but Gu tells WebMD that any hormonal birth control developed for non-Asian men is likely to include another hormone -- progestin.
Studies have shown the testosterone-progestin combination to be very effective in suppressing fertility in white men.
The Chinese men in Gu's study took monthly injections of 500 milligrams of TU in tea seed oil for 30 months. This formula is not available in the U.S. and is indicated to treat low testosterone levels with injections typically given every three months.
Over the course of the trial, nine pregnancies occurred in the partners of 1,045 study participants, or roughly one pregnancy for every 100 men.