TUESDAY, May 5 (HealthDay News) -- Injectable testosterone may be an effective form of male contraception, new research suggests.

Chinese researchers injected 1,045 healthy, fertile Chinese men aged 20 to 45 years with a 500 milligram formulation of testosterone undecanoate in tea seed oil once a month for 30 months.

All of the study participants had a normal medical history and had fathered at least one child within two years of beginning the study. The female partners of the study participants, aged 18 and 38 years, also had normal reproductive function.

Results showed a contraceptive failure rate of 1.1 per 100 men in the 24-month efficacy phase, resulting in pregnancy. The researchers noted that no serious adverse events were reported in any of the men and, in all but two men, reproductive function returned to the normal fertile reference range.

"For couples who cannot, or prefer not to use only female-oriented contraception, options have been limited to vasectomy, condom and withdrawal," said Dr. Yi-Qun Gu, of the National Research Institute for Family Planning in Beijing, China. "Our study shows a male hormonal contraceptive regimen may be a potential, novel and workable alternative."

The study will appear in the June issue of the Journal of Clinical Endocrinology & Metabolism.

This is the largest multi-center, male hormonal contraceptive efficacy clinical trial of an androgen preparation, Gu said in an Endocrine Society news release.

"Despite the present encouraging results, the long-term safety of this hormonal male contraceptive regimen requires more extensive testing with a focus on cardiovascular, prostate and behavioral safety," Gu said.

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