Depression study

A recent study conducted by Skovlund and colleagues at the University of Copenhagen examining the link between depression and hormonal contraception has received considerable media attention, but much of this coverage has taken the findings out of context. This article does not contain causal evidence that hormonal birth control causes depression. The study used Danish national health registry data to follow over 1 million women aged 15-34 from 2000 to 2013. The main purpose of the study was to compare first use of an antidepressant and first diagnosis of depression at a hospital psychiatric department between women using hormonal contraceptives and non-users (including women who had stopped use over 6 months ago and never users). Although this study included a large sample of women, it was only able to control for the factors available in the national databases and may have missed important factors that influence the development of depression, especially factors that may be shared between women who take hormonal contraception and women who develop depression. For instance, women using hormonal contraception might visit the doctor more regularly and therefore have a higher awareness of the symptoms of depression than non-users of hormonal contraception. For this reason, the results should not be taken as evidence that hormonal birth control causes depression.

The study found an increased relative risk of first use of an antidepressant (ranging from 1.1 to 2.0) and of first depression diagnosis at a hospital (ranging from 1.1-1.9)* among almost all users of hormonal contraception compared to non-users; however, the overall incidences of first antidepressant use and first depression diagnosis were low. The overall crude incidence rate of first use of antidepressants was 2.2 per 100 person-years among users of any hormonal contraceptive compared to 1.7 per 100 person-years among non-users, and the crude incidence rate of first depression diagnosis was 0.3 per 100 person-years among users of hormonal contraception compared to 0.28 per 100 person-years among non-users.

Putting this in perspective, this means among women who were not taking hormonal birth control in a given year, 1.7 out of 100 women would been given a prescription for antidepressants while among those women using any form of hormonal contraception, 2.2 out of 100 women would have been prescribed antidepressants for the first time.

Looking at oral contraceptives specifically, women taking combined pills (COCs) had an increased risk of first use of antidepressants of 20% (95% CI 22%-25%) compared to non-users of any hormonal contraception, while women taking progestin only pills (POPs) had an increased risk of 30% (95% CI 27%-40%) compared to non-users of hormonal contraception. In comparing COCs to POPs, it is important to note that only a small proportion of Danish women (4% of market share in 2010) used POPs as a method of hormonal birth control and use increased with age. Because POPs are more likely to be prescribed after birth while breastfeeding, the increased risk in depression may be partially due to a larger proportion of women in this group experiencing postpartum depression.** Researchers also found the highest relative risk for adolescents aged 15-19 with estimates of relative risk ranging from 1.4 to 3.1 for different types of hormonal contraception for first use of antidepressant and 1.2 to 3.2 for diagnosis of depression, with the highest risk amongst adolescents using the patch, ring, and IUD. In explaining this relationship, the researchers may have missed an important confounder: prior research has shown that adolescents who become sexually active are at a higher risk of depression and anxiety. Risks increased up to the first three to six months of use for all women and decreased thereafter.

These results must also be weighed against other studies. A study by O’Connell et al. in 2007 randomized 76 adolescent women to oral contraception or placebo for three months and found no significant difference in depressive symptoms. A study published in 1995 randomized 150 women who were sterilized or had partners that were sterilized to receive COCs, POPs, or placebo for four months and found POP users reported fewer depressive symptoms than those taking COCs or placebo pills. We highlight some of the higher quality studies, but they are part of a larger body of evidence that is conflicting and non-conclusive about the link between hormonal contraception and depression, as many of the studies conducted have been observational.

The recent study by Skovlund and colleagues does highlight that responses to hormonal contraception vary from person to person and emphasizes the need for all people to weigh the pros and cons of using any type of hormonal contraception and to consult a clinician if they have questions about certain side effects or risks. Physician and expert responses to this article highlight that women should not change their choice in contraception because of this study, and they should consider the benefits of each method of contraception alongside the potential risks of each option. Many thoughtful critiques and analyses have been written about this study that highlight many of the points raised here as well as others (e.g., Boston Magazine, The Establishment, Jezebel, and NPR).

*The estimated relative risk for one type of COC was less than one, but was not found to be statistically significant.
**The authors did exclude women during pregnancy and 6 months after.