Women have long borne the brunt of contraception responsibilities, but this may be shifting in coming years. A new trial published in the Journal of Clinical Endocrinology and Metabolism details strides made by researchers in developing a male version of the birth control pill, bringing it within reach of the long-sought-after FDA approval.

Like the female equivalent, a male oral contraceptive works by tweaking the body’s hormones to temporarily suppress fertility. In women, this involves introducing synthetic estrogen and/or progestin, which mimics progesterone, a hormone released in large amounts during pregnancy. When introduced into the female body, the pill stops ovulation, prevents sperm from entering the cervix, and thins the uterine lining, making implantation of a fertilized egg far less likely.

In men, the idea is to stop the production of sperm, which relies on both progesterone and androgens like testosterone.

The researchers developed 11-beta-MNTDC, a chemical cocktail that can mimic specific androgens and progesterone. These synthetic versions are agonists, meaning they can bind to the same receptors as natural chemicals, but they produce a different response from the body.

When introduced into men, 11-beta-MNTDC fills cells’ androgen and progesterone receptors, blocking the natural versions from being used and suppressing production of hormones necessary for sperm production, while allowing for the rest of the body to function normally.

In March the researchers presented the results of a 28-day trial during which they tested 11-beta-MNTDC on 40 healthy men. 10 of these men were given a placebo, while the other 30 were given varying doses of the drug. They found that the participants’ androgen levels fell more the higher the dose, with the average non-placebo participant levels falling below the limits of fertility.

Other male contraceptive trials have achieved similar results, but this trial is important because study participants had mild enough side effects to be seriously within reach of FDA approval. The only side effects reported were that five men claimed to have a decreased sex drive, two men claimed to have intermittent erectile dysfunction, and a handful of men reported mild headaches, fatigue, and acne.

Christina Wang, one of the senior investigators, claimed that there was little effect on libido for the majority of participants, which is often a source of concern for participants in these types of trials.

The side effects are much more limited than in previous studies, some of which were shut down due to concern about the participants’ safety. In particular, a study conducted by the World Health Organization testing a similar injectable contraceptive was abruptly halted when an independent review board determined that its risks outweighed its potential benefits. Though it had a 96 percent success rate among the 320 participants, this Phase II study was shut down after one participant permanently lost the ability to produce sperm, one participant committed suicide, and 20 left the study due to depression and other symptoms.

11-beta-MNTDC has thus fared far better than its predecessors, meaning it has gotten much further in the long and arduous process of getting FDA approval for a commercially available drug. However, this drug still needs a lot of testing before it is approved, especially because it’s still in Phase I.

One glaring omission from the trial that needs to be addressed in subsequent phases was that the participants’ sperm counts were not actually tested, only their hormone levels. The participants were not in the trial long enough to see significant effects on sperm production, as it takes 60 to 90 days and the study only lasted 28 days. However, researchers are confident that the measured drop in specific hormones is indicative of a drop in sperm production.

If they’re right and 11-beta-MNTDC is eventually approved, men would be able to shoulder more of the responsibility for oral contraception, as well as the side effects. Women—roughly 16 percent of US women according to the CDC—have dealt with the side effects of oral contraceptives, including headaches, nausea, weight change, irregular menstruation, mood fluctuations, an increased risk of venous thromboembolism or blood clots, decreased libido, and the potential for long-term mood disorders, among others.

The FDA claims these side effects are tolerated because, unfortunately, “the Pill was approved prior to revelations about the dangers of thalidomide and prior to passage of the 1962 Drug Amendments.” Therefore, hormonal contraceptives for men face far more scrutiny from the FDA, which explains the near-60-year disparity, not to mention the sexism involved.

Enovid, the original oral contraceptive pill, sparked widespread social change when it was first introduced in 1960, and although it probably won’t be as impactful, the male version, when it hits the market, could be a milestone in both social and sexual freedom.

The study’s co-senior investigator Christina Wang believes that “Safe, reversible hormonal male contraception should be available in about 10 years.”

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