An injection of progestin and a synthetic form of testosterone stopped pregnancy in 96% of female partners, the four-year worldwide study of 320 men in monogamous heterosexual relationships found.

Almost 75% of male participants reported being willing to use this method of contraception at the conclusion of the study.



But an independent committee stopped the trial for safety reasons after participants reported 1,491 adverse effects: 46% developed acne, 32% had mood disorders, and 23% had pain at the injection site. Twenty participants dropped out of the study due to side effects. Six men left due to changes in mood; six for acne, pain, or "panic" at first injections, palpitations, hypertension, or erectile dysfunction; and eight for more than one symptom. Researchers said nearly 39% of the symptoms reported were unrelated to the shots.

The study also raised concerns about the drug's impact on fertility; after one year, eight participants had not returned to fertility, and within four years one man had still only partially recovered his fertility.

The committee said "reports of mood changes, depression, pain at the injection site, and increased libido" were of most concern.

It's normal practice for medical studies to be cancelled when participants experience adverse side effects.

