Rachel Flink, MD
A new study recently came out linking hormonal birth control with depression, and people are understandably concerned. Many women feel blindsided, and doctors aren’t sure how to address these fears. However, a careful analysis of the study shows that some of the concerns may be overblown.
First, an overview of the study: Researchers used Danish medical records to see when women started hormonal contraception and when they received prescriptions for antidepressants, as well as certain information about the women themselves. The researchers then calculated the relative risk of starting antidepressants among users of hormonal birth control compared to non-users.
For the non-statisticians, relative risk is a way to compare the likelihood of different events (compared to a baseline risk of 1). Basically, you multiply the relative risk of some factor by the baseline rate, so a relative risk of 1.2 translates to a 20% higher risk of an event compared to the baseline. Depending on the absolute numbers, that may be highly concerning or not so much. If I told you there’s a one-in-a-million chance of getting a disease, but something gives you a relative risk of 2, meaning DOUBLE the chances, there’s still only a two-in-a-million chance of you getting that disease. Compare that to something with a one-in-ten chance of occurring, then adding a relative risk of only 1.2. In a population of a million people, the first example would only see one extra person get the disease, but the second example with a lower relative risk would see an extra 20,000 people affected. That’s why, even though relative risk is what is often reported, the absolute numbers really do matter.
Looking at the absolute numbers in this study, out of 1000 women aged 15-34 who were NOT using hormonal birth control, 17 started using antidepressants over the course of a year. So that’s the baseline rate. For 1000 birth control users, in addition to the 17 who would have started antidepressants anyway, three extra pill users, seven IUD users, 19 implant users, and 29 injectable contraceptive users began antidepressants. Out of 1000 teenage girls, only 9 non-users started antidepressants, so the baseline rate was much lower, but seven extra pill-users and 19 extra IUD users began antidepressants per year.
What this shows is that while the media has reported a 30% increased risk of depression among all contraceptive users, and a whopping 80% increased risk among teenagers, the absolute numbers are still quite small.
But hey, even if it’s only a few extra women, depression is bad, and birth control still causes it, right? Well, not exactly. There are other reasons to be skeptical about the conclusions in this study.
This study was an observational cohort study, which cannot show causation the way the “gold standard” randomized controlled trial (RCT) can. In an RCT, people are randomly assigned to different groups (i.e. pills vs. no pills), so any pre-existing differences among people should be randomly distributed and should not affect any group more than another. In a cohort study, however, researchers have no control over who starts birth control or what methods they choose. So the groups could have been different all along. Women who use hormonal contraception are already using the health care system – might they also be more likely to seek care for depression? Women who use non-oral methods (like the implant, IUD and injection) may feel more strongly about avoiding pregnancy, due to life or relationship stresses that can also make it harder to take pills regularly – might women with those stresses also have higher rates of depression? There are many plausible differences between contraceptive users and non-users, as well as women who choose different methods, which cannot be accounted for in this type of study.
So what do we do with this information? Is it completely revolutionary? Is it total crap?
Overall, this study raises some real concerns. Depressive symptoms are already listed as a potential side effect for all birth control methods, but it’s certainly important for women to discuss concerns and potential side effects with their doctors. The potential risks of birth control also need to be balanced with the risks of undesired pregnancy, which can both contribute to and be riskier in the setting of depression. So, talk to your doctor, and make sure you understand the choices you’re making. But, understand, there’s no bombshell here.
Rachel Flink, MD is an OB/GYN currently practicing in Western Pennsylvania and obtaining her Masters in Public Health at the University of Pittsburgh. Her clinical interests include reproductive health, pregnancy care, family planning, and minimizing barriers to care. Rachel’s research is focused on understanding women’s experiences with and preferences for reproductive health care. Outside of work, she enjoys reading, being active outdoors, and spending time with her husband, two-year-old son, and rambunctious dog.