Finally, an effective method of birth control for men may be on the way, Chinese researchers report in the Journal of Clinical Endocrinology and Metabolism.

The researchers found that monthly injections of testosterone are a "safe, effective, reversible, and reliable" means of contraception for men. However, the long-term effectiveness and safety of this treatment still needs to be established, they add.

Their findings are based on a study of 1,045 healthy fertile Chinese men. "We are satisfied with findings from this study," Dr. Yiqun Gu told Reuters Health.

"This male hormonal contraceptive regimen may offer a novel and workable alternative to existing family planning options for couples who can not or prefer not to use only female-oriented contraception throughout their reproductive years," added Gu, who is from the National Research Institute for Family Planning in Beijing.

The men in the study were between 20 and 45 years old and had fathered at least one child within the two years prior to enrollment in the study. Their female partners were between 18 and 38 years old and had normal fertility.

The men received monthly testosterone injections for 30 months. During the first 6 months, the men were tested to make sure that the injections had been effective in eliminating or markedly reducing the sperm levels in their semen. Only men with little or no sperm were allowed to continue into next 24 months of the study.

During the follow-up period, nine pregnancies occurred, which translates into a contraceptive failure rate of roughly 1 per 100 men. This rate, Gu said, is "excellent" compared with other contraceptive methods, including condoms and birth control pills.

No serious side effects were noted and after stopping the shots; sperm-making ability returned to normal in all but two men.

The investigators conclude that further study of testosterone injections is warranted to ensure long-term safety. Moreover, refinements are needed to make sure that all men have no sperm production while receiving this contraceptive.