Chinese researchers may have developed an injectable male contraceptive that is reversible and has few serious side effects, according to a report published in the Endocrine Society's Journal of Clinical Endocrinology & Metabolism.

The contraceptive is a combination of testosterone in tea seed oil. Chinese researchers conducted a study of 1,045 Chinese men between the ages of 20 and 45, in which each man had fathered at least one child. Each of the men had sexual partners between the ages of 18 and 38 years old.

The men were injected monthly with the formula for 30 months. At the end of the study, only one out of 100 men impregnated their partners. There were no serious side effects reported and reproductive function returned to normal levels in all but two participants, according to an Endocrine Society press release.

One of the researchers, Dr. Yi-Qun Gu, of the National Research Institute for Family Planning in Beijing, said despite the encouraging results, the contraceptive requires more testing on its effect on cardiovascular, prostate and behavioral health.