Scientists have developed a birth control injection for men that prevents pregnancy in their female partners, according to a study published in the Journal of Clinical Endocrinology and Metabolism.
In a healthy, fertile male there should be between 40 million and 300 million sperm per millilitre. The injectable hormonal contraceptive reduced this figure to just one million in 274 out of 320 study volunteers.
However, the researchers stopped recruiting new participants in 2011 due to the rate of adverse events, particularly depression and other mood disorders. Other side effects included injection site pain, muscle pain, increased libido and acne. There was one death by suicide in the group of volunteers, but this was assessed to be unrelated to the use of the drug.
The researchers studied the effects of the drug on men between the ages of 18 and 45 with normal sperm counts. They were given two hormone injections (progesterone and testosterone) once every eight weeks. Some study participants were asked to rely on the injection as their only form of contraception for up to one year. During this period, only four pregnancies were reported.
After the trial, the men were monitored to see how quickly their sperm counts recovered. One year later eight men had not recovered their normal sperm counts.
One of the study’s authors, Mario Philip Reyes Festin, 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. Our findings confirmed the efficacy of this contraceptive method previously seen in small studies.
‘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.’
Three quarters of the men who took part in the trial said they would be willing to use the method of contraception again, according to Allan Pacey, professor of andrology at the University of Sheffield.
This was a single arm prospective study looking at the contraceptive effect of two injections, one a synthetic progesterone (progestogen) called norethisterone enanthate and the other a testosterone derivative, testosterone undeconate, as measured by suppression of sperm production to infertile levels and pregnancy rates.
The initial results, compared to existing female-centred methods, are promising. This is especially the case compared to previous attempts at hormonal male contraception.
The combined failure rate was 7.5 per cent; even when failure was defined as the occurrence of pregnancy, the rate was still in excess of existing methods. These results by themselves mitigate against this method being applicable as a reliable male contraceptive method.
The concern here was the side effects; most men would not object to a method that increased libido but most would balk at mental health side effects which almost 40 per cent of trial subjects experienced, including mood swings, aggression and depression, not to mention increasing injection site pain.
While the era of hormonal male contraception is still not upon us, this study represents possibly the most promising method seen for many years, and the day when contraception is no longer the burden overwhelmingly of the female partner in a relationship is no doubt near.
Research score: 4/5