Up to this point, when it comes to birth control, women have more options than ever. Female contraceptives like the pill, intrauterine devices (IUDs), and hormonal implants have been widely used among women to prevent pregnancy. Meanwhile, male contraceptives have remained at a standstill, leaving men with two viable options: condoms or vasectomies to control their fertility. A recent study in the Journal of Clinical Endocrinology & Metabolism finds birth control shots may soon be on the horizon in preventing unintended pregnancies.

"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 study author Dr. Mario Philip Reyes Festin of the World Health Organization in Geneva, Switzerland, in a statement.

Over the years, there have been several attempts at developing a contraceptive for men. Researchers have tested several methods, including the male pill, and the male birth control shot, using synthetic hormones to temporarily block the effects of testosterone so the testicles stop producing healthy sperm cells. However, it’s been a difficult feat since men constantly produce sperm; they pump out at least 1,500 sperm a second, which makes blocking sperm from meeting the egg a challenge.

This needs to be achieved without lowering testosterone levels to the point where it can trigger side effects, such as a loss of libido. Researchers at the Guttmacher Institute believe the male birth control shot could be a viable contender.

In the study, the researchers tested the safety and effectiveness of injectable contraceptives in 320 healthy men ages 18 to 45. The participants were all in monogamous relationships with female partners between the ages of 18 to 38 for at least a year. The men were tested to ensure they had a healthy sperm count at the start of the study.

Healthcare professionals injected the men with 200 milligrams of a long-acting progestogen called norethisterone enanthate (NET-EN) and 1,000 milligrams of a long-acting androgen called testosterone undecanoate (TU) for up to 26 weeks to lower their sperm counts. Two injections were given every eight weeks; the participants provided semen samples after eight and 12 weeks in the suppression phase, and then every 2 weeks until they met the criteria for the next phase. The couples were instructed to use other non-hormonal birth control methods.

The couples were asked to solely rely on the injections for birth control once the men's sperm count was lowered to less than 1 million/ml in two consecutive tests. During the efficacy phase, the men continued to receive injections every eight weeks for up to 56 weeks, and then provide semen samples every eight weeks to ensure their sperm counts stayed low. After the injections were stopped, the men were monitored to see how quickly their sperm counts recovered.

The findings revealed the hormones were effective in reducing the sperm count to 1 million/ml or less within 24 weeks in 274 of the participants. This method was effective in nearly 96 percent of continuing users. Only four pregnancies occurred among the men's partners during the efficacy phase of the study.

However, due to the rate of adverse effects, specifically depression and mood disorders, the researchers stopped enrolling new participants. Of the 1,491 reported adverse events, nearly 39 percent were found to be unrelated to the contraceptive injections. These included one death by suicide which was assessed not to be related to the use of the drug.

Meanwhile, drug-related side effects included: injection site pain, muscle pain, increased libido and acne. Twenty men dropped out of the study due to the side effects. Despite the adverse effects, more than 75 percent of participants reported being willing to use this method of contraception at the end of the trial.

"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,” said Reyes Festin.

So, could this be better than the male pill?

Recently, researchers at Wolverhampton University have found a new compound that is able to deactivate the protein enabling sperm to swim. If a sperm cell can’t swim, the egg can’t be fertilized. This only lasts a few days, making men temporarily infertile. However, unlike the female pill, which takes a week to take effect, the compound may only take hours or minutes to activate.

The team behind the study will start live animal tests within the next two to three years. If this proves to be successful, the product could be on the market as a pill, or even nasal spray by 2021.

Men may soon have more of a say on their birth control options, whether they prefer the pill or a shot.

Source: Reyes Festin MP. Male birth control shots prevent pregnancy. Journal of Clinical Endocrinology and Metabolism. 2016.