Key Point: Two new studies show women on second-generation birth control saw more muscle growth than non-users over 12 weeks of lifting, but strength gains were exactly the same.
Oral contraceptives (OCs) change the hormonal environment for building muscle, but research on whether they help or hinder your gains is mixed.
Some studies find no difference, others a small benefit. One study found that birth control reduced gains after 10 weeks of training. In other words: mixed evidence.
Two new 2025 studies, both published in the Scandinavian Journal of Medicine & Science in Sports, suggest that for women taking a specific type of pill, the gains might actually be better.1 2
Let’s break down the science, the results, and the catch, without the technical jargon.
Study Setup: Who, What, and How Long?
Researchers wanted to see whether second-generation oral contraceptives give you a leg up or down in the gym compared to women with a natural menstrual cycle.
In the first study, they took 26 young, untrained women and split them into two groups:
- Team OC: 14 women on second-generation OCs (I’ll explain why the “generation” matters in a second).
- Team Natural: 12 women (non-users) with regular menstrual cycles.
Both groups followed a progressive full-body strength training program (2 sessions/week) for 12 weeks. The OC users completed two more sessions, on average, than the non-users (23 vs. 21).
In the second study, 15 OC users and 17 non-users followed a similar training program, also for 12 weeks.
The researchers measured muscle thickness using ultrasound (a reliable method for seeing inside the muscle) and checked body composition with DXA scans before and after.
The Results
After the 12 weeks of lifting, everyone gained muscle (as you’d expect in gym newbies). But the women on the pill gained significantly more.
First Study Results: Muscle Growth
Arm gains were the biggest, with the OC users seeing a 10.5% increase in lean mass compared to a 6.6% increase in the non-users.
The researchers also found that the OC group got greater hypertrophy in three other areas compared to the non-users:
- The supraspinatus (a part of the rotator cuff/shoulder) grew more than twice as much in OC users as in non-users.
- Total leg gains were similar, but the OC group saw greater muscle thickening in the vastus lateralis (the quad sweep) and the inner part of the gastrocnemius (calves).
The difference wasn’t tiny, either. The OC group saw greater gains, ranging from 4.5% to 7.9% in those muscles, while the non-users only saw gains of 1.5% to 3.1%.
Second Study Results: Muscle Growth
The results from the second study pretty much echoed those from the first.
- Larger increases in arm lean mass (5.5% vs. 2.9%).
- Better vastus lateralis growth (10% vs. 5.3%).
The Catch: More Muscle Didn’t Mean More Strength
You would assume that if your muscles get bigger, you would get stronger than the other group, right? Normally, yes, but not in this case.
Despite the OC group gaining significantly more mass, there was no difference in strength gains between the two groups. This held true for both studies.
Both groups in both studies got stronger because they were training, but the extra muscle size the pill users put on didn’t translate to measured strength on the dynamometer in any test.
Why Did The Gains Occur?
So, why did the participants in this study gain more muscle than those in similar, earlier studies?
The researchers speculate it comes down to the type of pill.
Second-generation pills use a progestin called levonorgestrel, which is androgenic, meaning it can bind to androgen receptors somewhat like testosterone does.
That way, it might give you a slight anabolic (growth) signal, even if it doesn’t make you stronger right away.
Birth Control and Muscle Growth: Takeaways
If you are on a second-generation pill (check your packet for levonorgestrel), you don’t need to worry about it killing your gains. On the contrary, it might help you put on a little extra lean muscle (the real-world differences are still modest even if the numbers look impressive).
If your main goal is powerlifting numbers, the pill probably won’t give you an edge, at least not short-term, but it won’t hurt you either.
These studies looked at second-generation pills. Third or fourth-generation OCs contain newer progestins (no levonorgestrel) and might not have the same effect.
For those newer pills and for the vast majority of women, the difference is likely negligible, and you can still get strong and build muscle while on them.
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Last reviewed: 2025-12-23
