Does Birth Control Affect Muscle Growth?

You're progressing in your strength training by gradually increasing variables like reps and sets, but you keep hitting a plateau that feels endless. Could your birth control pills be the reason?

Older research has suggested hormonal birth control could interfere with muscle mass, but it often left lifters with more questions than answers.

Here's what experts and more recent research has to say.

The question around birth control and muscle growth stems from mostly small, preliminary studies. For example, one published November 2021 in the ‌Journal of Strength and Conditioning‌ found oral contraceptive use impairs muscle gains in young women.

In that study, two small groups of women ages 18 to 29 — 34 who used birth control pills and 38 who didn't — did 10 weeks of resistance-training exercise. The researchers measured the women's body composition before and after and found significant differences in lean mass gains between the two groups at the end of the study period, particularly for women who had a higher amount of the synthetic hormone progestin in their contraceptives.

The researchers hypothesized the diminished lean mass gains could be related to how the pill affects hormone levels, including the way progestin may bind to certain androgen receptors — which help in hormone regulation and also play a role in muscle mass and strength — and inhibit their function.

The 'ideal pill' is one that's ideal for you specifically, not for a general goal like bodybuilding.

But that doesn't mean you should get off the pill if you want to build muscle mass, according to Jennifer Wu, MD, an ob-gyn at Lenox Hill Hospital in New York City. There are several caveats to keep in mind with this research, she says.

Most notably, the researchers included a small number of participants, and the study didn't fully explore the breadth of options when it comes to birth control pills. "There are so many doses and formulations of oral contraceptives that you can't group them all together under one definition in this way," Dr. Wu says. "You have different hormone levels in these contraceptives that are meant to mimic your own hormone levels so you're not experiencing a huge rise or fall as a result."

This study also doesn't tell us anything about other forms of hormonal birth control. "There are pills, but also injections, rings and an implant in the arm," Dr. Wu says.

Another detail to examine closely in birth control and muscle growth research is how mass was measured, says Khaled Zeitoun, MD, an ob-gyn and reproductive endocrinology and infertility specialist at New Hope Fertility in New York City.

"Previous studies measure the muscle mass itself but not the strength of the muscles," he says. "Research doing that doesn't find much difference between people taking pills and not taking pills." In other words, simply having slightly less muscle mass doesn't automatically translate to less strength.

For example, a May 2022 study in ‌BMC Women's Health‌ looked at whether oral contraceptive use affected muscle strength as well as muscle thickness, using leg press exercises as a measurement. Researchers measured muscle fibers for 74 young women — 34 were taking the pill and 40 were not — before and after 12 weeks of leg presses. Both groups showed increased muscle fiber size and strength.

This means there's no conclusive evidence muscle strength declines as a result of birth control pills, Dr. Zeitoun says. It is true that hormones related to muscle mass may be affected, he adds, but in terms of real-life effects, this shift doesn't seem to be a significant concern.

Also, Dr. Wu says, if the result of taking birth control pills was a considerable problem building muscle, then the thousands of athletes on the pill would be struggling. "Considering how many college and professional athletes are on birth control pills, and how many I have in my own practice, I think we'd hear about it if this was an actual problem," she adds.

Similar to the studies on building muscle and oral contraceptives, the effects of non-hormonal methods like a copper IUD have mixed findings.

In one April 2017 study in ‌Contraception,‌ researchers looked at the effects of three contraceptive methods: a hormonal implant, an IUD and a non-hormonal copper IUD. They measured changes in weight and body composition over the course of a year in 149 women. Lean body mass increased for the IUD users but not for those with implants. However, body composition in general didn't differ between the groups.

Another study, in an October-December 2016 edition of a Brazilian journal, ‌Revisa Brasileira de Educacao Fisica e Esporte‌, found women using a hormonal IUD lost 1.4 percent of their lean muscle mass after a year, compared to a 1 percent lean muscle mass loss among those using a copper IUD.

The takeaway from studies like these is that, again, individual results with any contraceptive method can vary, Dr. Wu says.

"Research is always important," she adds. "But in terms of using the findings to inform your decisions, it's going to come down to what works best for you on an individual level."

So, is there a "best birth control for bodybuilders" that anyone seeking to build muscle mass should pick? Not really, according to Dr. Wu. Even if you're seeing performance decreases in your strength training, it's likely your ob-gyn will want to consider all the possible reasons why before switching your birth control choice, she says.

"There are so many factors here, including the intensity of your training, how well you're sleeping, stress levels and nutrition, and all of those affect your hormone levels," she says. "Your contraception should be part of the conversation around your performance, but it's just one aspect to consider. Also, if you want to switch to something you think might work better, you have plenty of options."

For example, you might shift to a pill that has less progestin, the hormone singled out in older research as a potential link to less muscle mass, Dr. Zeitoun says. But even then, that's not a blanket recommendation for everyone who wants to build muscle. He adds that the "ideal pill" is one that's ideal for you specifically, not for a general goal like bodybuilding.

"Talk to your doctor if you think your pill is affecting your exercise outcomes," he says. "You might need to try several types of oral contraception before you reach the one that's right for you."