Learning Center

We believe that safe sports, good health decisions, excellent care and informed policy begin with education.

Can Birth Control Pills Prevent Knee Injuries?

Type into a search engine the query “Will birth control prevent ACL tears?” and the first result might read, “Another reason to take the pill.”

The answer, however, is more complicated.

Recent studies suggest that women taking birth control pills (also called oral contraceptives) are less likely to have surgery for a torn anterior cruciate ligament (ACL) than women not taking the pills. But two independent reviews say the studies suffer from critical shortcomings, and don’t prove that it’s the pills that are providing the protection.

Simply put, athletes should not take birth control pills for the purpose of preventing knee injuries.

Problem bigger than a pill?

The ACL is one of the ligaments that stabilize the knee during sports maneuvers such as cutting and pivoting. A tear to the ligament is a serious injury, and increases the chance of future knee problems, notably osteoarthritis. Recovery can take six months to a year whether the injury is managed with surgery or nonsurgical treatments. Yet surgery does not guarantee a pain-free, fully functioning knee or return to play.

For girls and women, ACL injuries have reached near-epidemic proportions. Women are two- to six-times more likely to suffer an ACL tear than men playing comparable sports. The reasons may have to do with the way girls and women run, jump, land, cut, and sense the position of their bodies and joints. Training programs can reduce the risk of an ACL injury, but they require time and commitment.

The research on birth control pills stems from the possibility that sex hormones could both contribute to the gender difference in ACL tears and also help to solve the problem.

Sex hormones and weak ligaments

In the research exploring whether birth control pills reduce ACL injury rates, women took pills that contained the hormones estrogen and progesterone. The pills prevent women from ovulating, or producing eggs, and suppress the hormone surge that accompanies it.

The logic of ACL injury prevention goes like this:

  • The ups and downs of hormone levels during the menstrual cycle may affect the laxity or stiffness of the ACL.
  • Fluctuations in female hormones could also alter neuromuscular function, or the ways female athletes maneuver, land and jump.
  • Greater ACL laxity and changes in landing and jumping techniques could increase the risk of ACL tears.
  • Taking oral contraceptive pills could suppress the hormonal surge and prevent ACL tears.

Two literature reviews published in 2017 say most of these statements remain theoretical. Both reviews examined the same body of research, with a particular focus on two large studies which showed that women who took birth control pills had a nearly 20% reduction in the risk for ACL surgery. One study was from the University of Texas and the other from Aarhus University in Denmark.

Best evidence falls short

The Texas and Danish studies each compared a large database of women who had ACL surgery with another large group of similar women who did not have ACL surgery. In both the surgery and nonsurgical groups, the researchers counted the number of women who received a prescription for birth control pills and the number who did not. They also examined a limited number of risk factors such as age that could increase the chance of an ACL tear.

In this type of study, researchers are limited by the information in a patient’s record. The researchers can’t evaluate other risk factors—for example, participation in sports—that might explain why some women tore their ACLs and some did not. Also, because the studies only looked at women who had surgery, the researchers could not assess the use of birth control pills among women with ACL injuries who did not have surgery.

For these and other reasons, say the reviews, the research poses problems.

  • In one of the independent reviews, researchers from Oregon Health & Science University rated the strength of the research using a widely accepted scale that classifies evidence as high, moderate, low or very low. “An important finding of our systematic review is our conclusion that the current quality of evidence is very low,” they wrote. “The true effect is likely to be substantially different.”
  • In another review, researchers from Brown University said their findings “do not support a protective effect” from taking birth control pills. “A better understanding of the relationship between oral contraceptive pill use and ACL injury is warranted.”

Because of the design of the studies and other concerns, the Oregon reviewers added that they had “very low confidence” in the reported benefit. “It is impossible to assign cause and effect,” they wrote. In other words, the research doesn’t meet the standard for proving that the protection from ACL surgery observed among birth control users was caused by pills and not something else.

Proving the effectiveness of an injury prevention program takes a great deal of time, effort and resources. The Oregon team recommends a large carefully controlled study that follows elite athletes over time to see if those who take birth control pills suffer fewer ACL injuries than others. Such a study would need to eliminate a broad range of problems that have hampered the strength and quality of previous research. Until then, questions about the protective prowess of pills remain.