How Oral Contraceptives Impact Your Gut Microbiota

When the birth control pill was introduced in 1960, it heralded a new era for sexual and reproductive health. Fifty-eight years later, scientists are discovering that the effects of oral contraceptives may extend beyond simply preventing pregnancy: they also impact the gut microbiota in numerous ways.

With an estimated 16 percent of the affected population aged 15-44 taking hormonal birth control pills, it’s more important than ever to understand how oral contraceptives can affect a person’s overall health, beginning in the gut.

Throughout the years, the scientific community has done a number of studies about the use of the pill and its effect on inflammatory bowel diseases (IBD), including Crohn’s disease. While the studies may differ in their focus, methods, tenure, and sample size, they all point to one common conclusion: there is a direct link between oral contraceptive use and your gut.


The estrogen connection

While estrogen-free birth control pills exist, most oral contraceptives contain a form of the hormone. Estrogen can have an impact on the way material travels through your gut wall and into the rest of your body.

Oral contraceptives may also increase the risk of IBD. Sex hormones (including estrogen) in your gut microbiota can also affect the development of autoimmune diseases.

In a 2016 paper, Dr. Hamed Khalili, a gastroenterologist, reviewed evidence from numerous studies about IBS and hormonal birth control pills and found a link between the gut microbiome, oral contraceptives, and the body’s immunity levels. “This supports the intriguing hypothesis that the gut microbiome lies at the crossroads of pathways linking exogenous hormone use with innate and adaptive immunity,” Khalili stated. Further, a 2016 study in which Dr. Khalili was the lead researcher found that if you already have Crohn’s disease, taking the pill can increase the need for surgery.


Who knew the pill affected your gut microbiome so much?

In his literature review, Dr. Khalili suggests that, beyond smoking, the use of oral contraceptives is perhaps the most consistent environmental risk factor for Crohn’s disease. He cautions, however, that the sample sizes for previous studies are too small to be completely conclusive.

Two long-term studies–one begun in 1976, the other in 1984–tracked more than 200,000 women who were using oral contraceptives to see if they developed IBD. While research found that women who took hormonal birth control pills were more likely to develop IBD, it’s important to note that the women who were more likely to develop Crohn’s disease also had a history of smoking.

The findings coincide with rumblings that began in the scientific community in the late 1960s about the connection between IBD and oral contraceptives; however, there are a couple of other factors to consider when evaluating this information.

First, it’s important to note that the pill that existed during these studies is a lot different from the pill that doctors prescribe today. Estrogen levels in oral contraceptives are significantly lower in the 2010s than they were in the 1960s. Also, as noted, fewer women were on the pill when the studies began, meaning the sample size was relatively small.

Finally, a 2008 study found that the time a woman take hormonal birth control pills matters: longer-term use can result in a higher risk of developing Crohn’s disease or another form of IBD.


Weighing the risks of oral contraceptives

Currently, the data points to a strong association between oral contraceptives and Crohn’s disease; however, there is not enough of a risk that doctors recommend that their patients—even those at higher risk of developing Crohn’s disease—use a different birth control method. There is enough evidence, however, to support the need for keeping the gut microbiome healthy while taking an oral contraceptive.

The pill is the greatest single advancement in the entire history of reproductive health. Fifty years of research, however, shows that oral contraceptives can impact the gut microbiome and may increase the risk of developing IBD. Until there is conclusive data on just how extensive those risks are, it’s a good idea to pay extra attention to the health of your gut microbiome. Whether taking an oral contraceptive or not, a healthy gut is always a good thing.