HealthDay News — A contraceptive injection for men shows some promise, but researchers are still struggling to improve its effectiveness and deal with severe side effects caused by the injections, according to a study published online October 27 in the Journal of Clinical Endocrinology & Metabolism.

Researchers recruited 320 healthy men aged 18 to 45 from seven different countries across the world. The participants all had normal sperm counts and had been in monogamous relationships with female partners between the ages of 18 and 38 for at least a year. The men received the testosterone/progestogen injections every eight weeks. 

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The combination lowered sperm counts to the targeted goal – <1 million/mL – in 274 of the men. Four pregnancies occurred among 266 men continuing to receive the treatment, an effectiveness rate comparable to other contraceptive methods. There were 771 incidents of side effects assessed to be either likely or definitely related to the injection. The most common were acne, increased libido, muscle pain, and mood and emotional disorders. Twenty men dropped out of the study due to side effects, and the adverse events eventually led to the early end of the study.

“The safety committee felt that the number of side effects, particularly the mood changes, were too many,” researcher Mario Festin, MD, a medical officer with the department of reproductive health and research at the World Health Organization, told HealthDay. The committee also felt “at that point, the study had already proven that the drug combination could already produce the desired effect of lower sperm counts, and the unfavorable side effects may outweigh any further findings.”

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