This might come as good news for women on birth control and looking for an alternative - an injected male contraceptive has been shown to be almost 100% effective in a trial involving 350 men.
The hormone-based jab is designed to lower sperm count by acting on the brain.
It contains a long-acting form of progestogen - a hormone which blocks sperm production controlled by the small pituitary gland - as well as some testosterone to counter-balance the reduction in levels of the male hormone.
Over a year-long trial, nearly 96% of couples relying on the injection to prevent unplanned pregnancies found it to be effective. Four pregnancies occurred among the men's partners during this time.
But before anyone gets too excited, researchers have said more work is needed to address the treatment's reported side effects, which included depression, other mood disorders, muscle pain, acne and increased libido.
The side effects were enough to make 20 men drop out.
After an initial period where couples used the injection as well as other birth control methods, the men entered the study's "efficacy phase" - a year-long timeframe where jabs were the only form of contraceptive used, injected into the men every two months.
In 274 men, the injection reduced sperm count to one million per millilitre or fewer within 24 weeks.
Scientists actually stopped enrolling new participants into the study in 2011 because of the rate of apparent side effects.
Of the 1,491 incidents, nearly 39% were found to be unrelated to the treatment - including one suicide.
One man experienced an abnormally fast and irregular heartbeat when he stopped receiving the injections.
But by the end of the trial, three-quarters of the men said they would be willing to continue using the contraceptive jab.
The results are reported in the Journal of Clinical Endocrinology & Metabolism, published by the Endocrine Society.