*The first male contraceptive clinical trials
The first clinical trials for male hormonal contraceptives hail back to the 1970sTrusted Source. Male hormonal contraceptives have the aim of interfering with testosterone production and ultimately stopping the production of sperm.
Without sperm in the semenTrusted Source, or seminal fluid, the fluid that typically comes out of the penis at ejaculation, and which acts as a carrier vehicle for the sperm, there is no danger of fertilizing ovules, or eggs, produced by the ovariesTrusted Source, which results in pregnancy.
The first male hormonal contraceptives to be tested were injection-based, they appeared to be ultimately safe and effective, and the trial participants were able to produce sperm again once they stopped receiving the injections.
Yet several participants discontinued their involvement in these early trials due to the fact that it took a long time for the injections to take full effect and stop the production of sperm, and because they had a “dislike of the injection schedule.”
Later trials — in the early 2000s — tested the efficacy of hormonal contraceptive implants, though often they still required an additional injection protocol.
Studies showed that the participants did not experience any serious side effects, and the contraceptive method appeared effective, yet many of the male participants dropped out, reportedly due to study “protocol-related reasons” and “altered personal circumstances.”
While all this research provided key information about what might be effective and what not, none of them got very far, as the frequency of the required injections put off many of the study participants.
What happened to more recent studies?
Data from one of the more recent studies that promised an effective contraceptive for males were reported in The Journal of Clinical Endocrinology & Metabolism in 2016. This phase 2 clinical trial tested an injectable combination hormonal contraceptive in a group of 320 healthy volunteers aged 18–45 years.
An injection with too frequent side effects
The injection — administered once every 8 weeks — contained norethisterone enanthate and testosterone undecanoate, and its aim was to suppress sperm production.
The study concluded that the contraceptive was effective in reducing sperm production almost to nil, and confirmed that this effect was reversible — all of which was good news. However, it also issued an important caution: Among the participants, there was a high “frequency of reported moderate and severe mood disorders including depression” linked to the use of the injectable contraceptive.
Despite the promising results on efficacy and overall safety, this male contraceptive candidate never made it to the market. Why? The obvious answer seems to be that the participants were uncomfortable and unwilling to put up with the reported side effects — indeed, 20 of the original 320 participants dropped out of the trial for this reason.
Yet the answer may not be as simple: Reportedly, around 75% of the volunteers said they would be happy to continue on the contraceptive at the end of the trial. So if the participants themselves were willing to continue, why did the researchers put an end to the trials? The answer is in the study paper itself.
The WHO Department of Reproductive Health and Research had established an independent Data Safety and Monitoring Committee to assess the trial results, as the WHO was one of the co-sponsors of the study.
In the study paper, the authors note that, in 2011, the external monitoring committee determined that “for safety reasons, recruitment [of further participants for the clinical trials] should be stopped and enrolled participants should discontinue receiving injections and be transitioned to the recovery phase” because, in their estimation, “the risks to the study participants outweighed the potential benefits.”
Since then, several studies on both hormonal and nonhormonal contraceptive candidates have made the headlines, all promising the imminent advent of a commercially available male contraceptive.