A New Male Birth Control Works in Mice. Will It work in Humans?

When it comes to preventing pregnancy, there are several birth control options to choose from—if you’re female, at least. Birth control pills, implants, vaginal rings, shots, patches, and intrauterine devices (IUDs) are available for females, but birth control options are much more limited for males.

Melanie Balbach, PhD, a reproductive biologist and postdoctoral associate in Pharmacology at Weill Cornell Medicine, told Verywell that “men really only have two options: condoms and vasectomies.”

There’s been more research to find male birth control options in recent years—and a new study in mice led by Balbach looks very promising.

Preventing Pregnancy—In Mice

Balbach’s team designed a new drug candidate to briefly block male sperm and prevent it from swimming. When they tested the preclinical drug in mice, they found that it was 100% effective at preventing pregnancy.

The researchers injected the non-hormonal drug candidate into male mice, who were then paired up with female mice. None of the females in the 52 pairs the researchers tested got pregnant.

Within 2.5 hours of injection, the drug was considered 100% effective at preventing pregnancy. Within 3.5 hours, it was 91% effective.

The mice who did not get the drug impregnated female mice 30% of the time.

“When we gave our inhibitor [drug] to the mice and paired them with a female for 2.5 hours, within that window, we didn’t get any pregnancies,” said Balbach.

According to Balbach, the sperm in the male mice essentially “stopped swimming within 30 minutes” of getting the injection, but by 24 hours, “their fertility returned.”

How Does The Drug Work?

Balbach explained that when sperm is made in the testes, they get stored in an organ next to the testes called the epididymis where they wait to be ejaculated. As soon as they are ejaculated, the sperm start moving and swim to the entrance of the vagina, then all the way up to the uterus. 

The drug candidate in the study works by blocking a protein called soluble adenylyl cyclase (SAC), which helps control sperm motility and movement. If that protein could be blocked in humans like it was in mice, the sperm would never make it out of the vaginal canal past the cervix and into the uterus.

“SAC is the ‘on switch’ of sperm which controls the onset of motility,” said Balbach. “With our inhibitor, we’re actually blocking SAC and are thereby blocking the activation of sperm motility. This means the sperm will be trapped in the vagina and can’t go into the uterus and up the female tract.”

Balbach said that the team expects they would see similar findings in human clinical trials for their drug candidate as they did in mice.

The researchers noted that the preclinical drug is also non-hormonal, which means it does not interfere with the hormones in the body—unlike hormonal birth control pills.

In addition, Balbach said the team wants to design the drug so it wouldn’t need to be taken every day like birth control pills. Instead, it could be taken as often as a person wanted to have intercourse.

“Our approach—hopefully when it ends up being in humans one day—can be on demand and quickly reversible so the men only take it when they need to block the fertility and don’t take it when they want to have a baby,” said Balbach. “We just want to be one of many options out there and maybe there will be a hormonal option for men depending on their needs.”

According to Balbach, the team is now testing the drug candidate in rabbits. The goal is to start human clinical trials in the next few years.

“We’re currently making sure that we’re using the ideal inhibitor, which then can become a drug,” said Balbach. “It needs to be tweaked a little bit more to become perfect because that’s what we want to do before we start clinical trials.”

Males Have Limited Birth Control Options

Celia Santi, MD, PhD, associate professor of obstetrics and gynecology at Washington University School of Medicine, reiterated that there are currently just two contraception methods available for males: condoms and vasectomies.

Condoms

According to Santi, condoms act as a physical barrier to prevent semen from being deposited into the vaginal canal.

Latex condoms can help prevent pregnancy and protect against many sexually transmitted infections (STIs), including human immunodeficiency virus (HIV).

According to Santi, while condoms are relatively free from side effects, they do have a failure rate of 13% with typical use.

Vasectomies 

Bobby Najari, MD, director of male infertility at New York University’s School of Medicine, told Verywell that a vasectomy is considered a permanent method of contraception. It is a minor surgical procedure that prevents sperm from being ejaculated from the penis.

The surgery is done by cutting and sealing the vas deferens—the tubes that transport sperm after they leave the testicles.

“This blockage results in a minor decrease in the amount of fluid that is ejaculated (5% less), but has no effect on sexual function or male health,” Najari said.

What About Pulling Out?

Removing the penis from the vagina before ejaculation (the withdrawal method or “pulling out”) is technically another option for people with a penis—but not a recommended one.

However, Sarah McBane, PharmD, associate dean of pharmacy education at the University of California, Irvine, School of Pharmacy & Pharmaceutical Sciences, told Verywell that withdrawal is not very effective and does not protect against STIs.

One reason withdrawal is a risky birth control method is that the penis may not be removed from the vagina before pre-ejaculate (“precum”) is released. The fluid usually does not have sperm in it, but that’s not always the case.

A person also can’t control when it’s released and may not realize that it has been. So, while the risk of pregnancy from pre-ejaculate is low, it’s never zero.

Why We Need Male Birth Control

Considering the lack of choice among male birth control, experts are calling for more male birth control options that are non-permanent and more effective. 

“The only other method of contraception for males beyond condoms or vasectomy would be abstinence,” said McBane. “Other currently marketed contraceptive options, such as pills and implants, are used by females.” 

McBane pointed out that having more than a handful of options is important because there can be many factors that could prevent a couple from using the options that are available.

For example, a female partner might not be able to safely use hormonal contraception or a partner could have an allergy to the latex in most condoms. 

While females still carry a disproportionate burden in reproductive health and contraception (partly because they have more options), Najari said there is growing interest and a cultural shift toward males contributing more to contraception, particularly “after recent changes to the legal landscape regarding abortion.”

A report by the Male Contraceptive Initiative found almost 50% of men ages 18–49 in the United States who have sex with women and who do not wish to father a pregnancy express a high level of interest in novel male contraceptives.

“Across the nation—and particularly in states where abortion is more limited—health care providers are seeing an increase in vasectomy volume,” said Najari. “I have no doubt that if there were a non-permanent male contraceptive option available, many men would utilize it.”

How Long Before Male Birth Control Is Available?

According to the Food and Drug Administration (FDA), the average time it takes to bring a new drug to market is about eight and a half years.

Once a drug has met all the requirements for safety and effectiveness in animal studies, there are three study phases it will still need to go through before it could get FDA approval.

While we might still be years away from mice birth control making its way to humans, the study is a step in the direction researchers want to be heading in.

“The development of a non-hormonal male contraceptive with no considerable side effects that can act on demand and be fully reversible is a great start,” said Santi. “More involvement of pharmaceutical companies, regulatory guidance, fair pricing, and health care coverage would be critical to ensure the development of male contraceptives, having an impact on reproductive care and global health.”