A male contraceptive jab has been shown to be almost as effective as the female pill in a trial that could pave the way for men and women being able to share equal responsibility for birth control.
In the study, 350 men were given injections of hormones that were shown to dramatically lower their sperm count by “switching off” the male reproductive system. The drugs caused some unpleasant side-effects, however, meaning that the trial had to be halted early.
The men, who were all in long-term relationships, relied on the drugs to prevent unplanned pregnancies – and the combination of hormones was found to be nearly 96% effective.
Richard Anderson, a professor of clinical reproductive science and author of the study, said: “If you’re comparing it to other reversible male methods, it’s far better than the condom and it puts it in the same ballpark as the pill.”
However, the treatment was judged to have unacceptable side-effects, including depression, acne and increased libido, which caused 20 men to drop out of the study and ultimately led to the trial be stopped earlier than planned.
The trial involved injections of two hormones. A long-acting form of progestogen was designed to act on the pituitary gland to switch off sperm production. Testosterone was added to offset a drop in the male hormone triggered by the progestogen. “You need the testosterone to feel OK,” said Anderson.
After an initial period, when couples used both the injections and other birth control methods, the men entered the study’s “efficacy phase”. This lasted up to a year and the men relied on the jabs alone, which they received every two months.
Only four pregnancies occurred among partners of the 274 men, indicating a similar level of efficacy to the female combined pill and significantly better protection than condoms, which in real-life conditions are about 82% effective.
However, scientists stopped enrolling new participants into the study in 2011 due to the rate of reported side-effects.
Of the 1,491 incidents, 39% were found to be unrelated to the treatment. This included one suicide. One man experienced an abnormally fast and irregular heartbeat when he stopped receiving the injections.
Despite the side effects, at the end of the trial, three-quarters of the men said they would be willing to continue using the contraceptive jab. The scientists said it might be possible to reduce the side-effects by changing the dose of hormones or the way they are delivered.
“The results provide us with confidence that this can be done,” said Anderson.
He added that it would be difficult to convert the treatment to a pill form because the hormones are quickly metabolised by the liver, but the scientists are planning a new trial in which the combination is delivered through a gel that the men could rub on their chest each morning.
Other scientists were less convinced that the side-effects of could be overcome, however. Sarah Jones, a reader in pharmacology at the University of Wolverhampton, said: “Most previous attempts at male contraception that have involved hormonal targets have led to severe side-effects or have been irreversible. This study does seem better than previous ones, but it still doesn’t seem very good to me.”
Jones recently published research demonstrating that certain compounds could be used to impede sperm’s ability to swim, which she argues offers a more realistic route to reversible male contraceptives in the future.
Allan Pacey, professor of andrology at the University of Sheffield, agreed that the side-effects found in the study were a “major concern”. However, he said the efficacy was impressive. “Using long-acting injectable forms of [progestogen and testosterone] the authors were able to suppress the production of sperm to a remarkable degree,” he said. “As such, this contraceptive was extremely effective and therefore certainly has promise.”
The findings are reported in the Journal of Clinical Endocrinology & Metabolism.
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. Additionally, the fact that the study reports relatively low side-effects and good ease of use are real-world developments. The study involved a reasonable number of patients so the results are likely to be robust.”