The injection helps block sperm production by impacting the brain’s pituitary gland.
But while the new jab shows promise, scientists said more work needs to be done to address its side effects, which included depression, muscle pain, acne and increased libido.
Following the year-long trial, 96% of couples relying on the injection to prevent unplanned pregnancies found it to be effective.
During this time, only four pregnancies occurred among the men’s partners.
To put it into context, the female contraceptive pill, if taken correctly, is 99.9% effective.
The side effects of the injection - including depression and other mood disorders, muscle pain and acne - caused 20 men to drop out of the trial.
“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,” said Dr Mario Festin, from the World Health Organisation, according to the Press Association.
“Our findings confirmed the efficacy of this contraceptive method previously seen in small studies.”
Dr Festin added: “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.
“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.”
At the end of the trial, three quarters of the men said they would be willing to continue using the contraceptive jab.
Fertility expert Professor Allan Pacey, from the University of Sheffield, hailed the fact that 75% of men would be willing to continue using the contraception as “noteworthy”.
He added, however, that the side effects are concerning and need to be addressed.
“For a male contraceptive to be accepted by men (or women) then it has to be well tolerated and not cause further problems,” he said. “For me, this is the major concern of this study.”
Scientists are also currently developing a male pill, which could become a reality in the next five years.
New research from the University of Wolverhampton has found a way to ‘switch off’ sperm. The peptide-based treatment, which acts as a ‘Trojan horse’, invades cells and turns off sperm almost instantly.
Because of this, the pill could be taken right before sex (in a form such as nasal spray or pill) and the effects can last up to a couple of days.
Professor John Howl, from the University of Wolverhampton, said: “The results are startling – and almost instant. When you take healthy sperm and add our compound, within a few minutes the sperm basically cannot move.”
The study’s findings have been published in the Journal of Clinical Endocrinology and Metabolism.
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