I was on vacation and off the grid last week. So I missed posting on some stuff. Like this, which originally appeared on The Upshot (copyright 2017, The New York Times Company).
One of the biggest American public health victories of the last decade has been the record low reached in the teenage birthrate. Along with that have been lows in rates for teenage pregnancy and abortion. Most researchers believe that improved access to contraception is a large part of this success.
But news continues to focus on the concern that hormone-based contraception — like the pill or the patch — causes depression, and that this should lead us to question its wider use. A more nuanced discussion would consider both the benefits and the harms.
This issue drew widespread coverage at the end of last year with a large study published in JAMA Psychiatry. Researchers tracked all women and adolescent females (ages 15 to 34) living in Denmark from 2000 through 2014. The study found that those who used hormonal contraception had significantly higher risks of also taking an antidepressant.
The study broke down the increased relative risk for each hormonal method this way: combined oral contraceptives (23 percent), progestogen-only pills (34 percent), the patch (100 percent), vaginal ring (60 percent) and levonorgestrel intrauterine system (40 percent).
The risks were highest in adolescents and decreased as women aged. The risks also peaked six months after the start of contraception.
Needless to say, many news outlets covered this finding widely. Some portrayed it as shocking new information that should change the way we think about hormonal birth control. Others saw it as a vindication of many women who said for years that birth control had triggered their depression while scientists and doctors ignored them.
But we have to acknowledge the limitations of this type of research. It’s not a controlled trial, and it’s impossible to establish causality. Women who choose to have sex could also be more likely to consider antidepressant use. Women who are plugged in enough to the health care system to obtain hormonal contraception could be more likely to have their depression appropriately diagnosed and treated — which is a good thing.
It’s also possible that an antidepressant prescription isn’t the best measure of new-onset depression. That would require an actual diagnosis by a health care professional, and such data were not available in the Danish cohort.
Previous studies that looked at rates of severe depression did not find a correlation with hormonal birth control use. Finally, huge cohort studies using many participants are likely to find a statistically significant result even if that result is not clinically significant. This is especially true if the cohort data come from an administrative database, like the one used in this study, that has been specifically identified as problematic in prior publications.
We also have to place this study in context with others. Months earlier, a systematic review of all studies that looked at the relationship between hormonal contraception and depression was published in The European Journal of Contraception and Reproductive Health Care. The authors first noted that there were too few prospective studies. But the data that do exist show that most women don’t show any effect from hormonal birth control, or actually had their mood improve.
Adverse effects were rare, and even rarer when the contraception contained lower levels of the hormone progestin. Finally, women who have underlying mood disorders were more predisposed to have mood-related side effects, but that could be related to their choosing different types of birth control rather than the birth control itself.
When many studies do not find a connection, and then one does, that latter one does not “replace” all prior research. That study has to be weighed along with the rest. It’s also important to consider publication bias, in which a study is more likely to be published if it’s a “significant” result and if it’s newsy. In this case, the finding that common birth control causes depression is both.
But let us assume, for the sake of argument, that this most recent finding is both real and causal. Even then, we need to rely on absolute risks, not relative risks. In the Denmark study, for every 100 women who didn’t use hormonal birth control, 1.7 were later prescribed an antidepressant. For every 100 who did use hormonal birth control, 2.2 were later prescribed an antidepressant. The overall difference (0.5 percentage points) means that if this were a randomized controlled trial, we would expect that for every 200 women treated, one extra woman might need to be treated with an antidepressant.
We can also assume, though, that pretty much all of them would receive the benefit of birth control in family planning. Moreover, lest anyone forget, depression is also significantly associated with pregnancy, especially when that pregnancy is unintended.
None of this is to say that we should ignore the risk of depression. Depression is a listed side effect of birth control; it’s on the package inserts.
All drugs have side effects. The drug I take for my ulcerative colitis has a real, if small, risk of causing myelosuppression. But the benefits I receive from it simply outweigh the risks.
Women need to discuss with their physicians the potential downsides, as well as the potential upsides, of all forms of contraception. We shouldn’t ignore the potential for hormonal birth control to cause mood changes in women. We also shouldn’t pay attention only to those side effects, forgetting to place them in context with the benefits.