The male contraceptive is administered as a jab WestEnd61/REX/Shutterstock

An injected male contraceptive has been shown to be almost 100 per cent effective in a trial involving 320 men.

The hormone-based jab is designed to lower sperm counts by acting on the brain’s pituitary gland.

Over a year-long trial, the injection was effective in nearly 96 per cent of couples. However, researchers said more work was needed to address the treatment’s reported side effects, which included depression and other mood disorders, muscle pain, acne and increased libido.


The side effects caused 20 men to drop out of the trial. There was one case of depression, one intentional paracetamol overdose, and one case of an irregular heart rate – all judged as being possibly related to the injection.

The trial was eventually discontinued after an external panel of reviewers concluded that the risks to the study participants outweighed the potential benefits. Nevertheless, more than 75 per cent of men in the trial said they were satisfied with the injection and would continue to use it if it were available.

Mario Festin, from the World Health Organization said: “The study found it is possible to have a hormonal contraceptive for men that reduces the risk of unplanned pregnancies in the partners of men who use it.”

The injections contained a long-acting form of progestogen, a hormone that has the effect of blocking sperm production controlled by the pituitary gland. Testosterone was added to counter-balance reductions in levels of the male hormone resulting from the treatment.

After an initial period during which couples used both the injections and other birth control methods, the men entered the study’s “efficacy phase” and relied on the jabs alone.

Side effect concern

Throughout the efficacy phase, which lasted up to a year, the men were given injections every two months. During this time four pregnancies occurred among the partners of 266 participants – a rate of 1.57 per 100 users. The combined contraceptive pill, for comparison, has a rate of less than 1 pregnancy per 100 women who use it.

“More research is needed to advance this concept to the point that it can be made widely available to men as a method of contraception,” says Festin. “Although the injections were effective in reducing the rate of pregnancy, the combination of hormones needs to be studied more to consider a good balance between efficacy and safety.”

Chris Barratt, professor of reproductive medicine at the University of Dundee, said: “This is high-quality research from a very experienced group of investigators, and as there has been no progress in male contraceptives for 40-plus years this is a very significant and welcome development.”

Leading fertility expert Allan Pacey, from the University of Sheffield, said the evidence showed the injections to be “extremely effective” but he was concerned about the side effects. “For a male contraceptive to be accepted by men (or women) then it has to be well tolerated and not cause further problems. For me, this is the major concern of this study.”

Journal reference: Journal of Clinical Endocrinology & Metabolism, DOI: 10.1210/jc.2016-2141