For anyone taking hormonal birth control, it must’ve been a scary week. “Contraceptive pill causes depression”, “Contraceptive pill is linked to depression”, and “The pill is linked to depression” are some of the headlines that have been blaring from almost every news source since a large Danish study was released at the end of last week about the contraceptive pill in Danish women.
I can only imagine that, for the ~50% of women who use the pill for contraception, it’s been pretty frightening to hear.
But is there really anything to worry about?
There are many acknowledged side-effects of taking the pill; I’ve heard stories of terrible cramps from one pill or another, really bad headaches of varying length and severity, and a bunch of other equally nasty things that are now widely accepted and documented risks. There’s also a lot of evidence that the pill increases your risk of certain cancers (mainly breast) although this is balanced against the fact that it also protects against other cancers (ovarian, womb and possibly bowel) and also that your risk of cancer goes away once you stop taking the pill. It’s also well demonstrated that hormonal contraception increases your risk of some heart conditions.
The short story is that anything you put in your body which has one effect (stopping pregnancy) will often come with an increased risk of having bad things happen too (painful cramps).
The other side of the coin is that the pill also has a lot of unintended good side-effects (for some) like treating acne, making periods less painful, reducing the risk of menstrual migraines, and the cancer risk reductions I’ve already mentioned.
Recently there has been increasing attention on one of the major side-effects of the pill; mood changes. Hormones have a massive effect on our mood (just look at any hormonal teenager) and it’s not really surprising that if you change the amount of hormones in your body, there will be some effect on your mood as well.
The hypothesis that the large Danish study was testing was that taking the pill would increase your risk of depression. It’s not a crazy idea, particularly because women are twice as likely as men to suffer from depression, and because hormonal changes have been linked to depression before.
Depression in Denmark
The first thing to mention is that the study in question wasn’t just big; it was huge. Using national registers, the researchers were able to analyze the records of more than 1 million women (basically a statistician’s wet dream). This covered almost the entire population of women in Denmark of the included ages over the study period. To put it in context, I recently celebrated getting 10,000 records for a study I’m involved in with cheering and beer.
So with their beautifully large sample-size, and linkage of several big national databases, off down the yellow brick road of science the researchers went.
And here they came to their first hurdle.
It’s a bit difficult to estimate rates of depression. People who are diagnosed in hospital represent a tiny fraction of those suffering, but accessing diagnostic records for every primary care facility where people might have been diagnosed is incredibly hard. And even then, many people who suffer from depression are never diagnosed. In this study they used what are known as surrogate endpoints; basically measurable differences that probably affect the disease in question, but might not.
In this case, the main thing that was measured was how many people had been prescribed antidepressants.
Now there are some problems with that (one even acknowledged in the study itself). Firstly, antidepressants are prescribed for a lot of conditions these days, with drug companies marketing them for everything from eating disorders to panic attacks to bipolar disorder. So knowing that people are more likely to be prescribed antidepressants doesn’t necessarily mean that they are more likely to have depression.
Secondly, people who are prescribed any medication are often different to people who aren’t. In fact, the study noted that the women on the contraceptive pill were more likely to have lower education levels. Something that they failed to mention was that low levels of education are also associated with depression. In fact, aside from age, there was little analysis of any social factors of depression in the study, despite the fact that social factors play a huge role in mental health. It may just be that people who take the pill are also more likely to take antidepressants for a whole range of social reasons — from this study, we just don’t know.
This was also an observational study; women weren’t randomly assigned into groups, there was no screening for depression at the start to exclude people who had undiagnosed illness, and there was no blinding (everyone who took the pill knew what they were taking). In practical terms, this means that the results are likely to be overstated, although to their credit the researchers did as much as they could to minimize these problems.
All of this aside, the researchers found that there was an increase in the rate of antidepressant prescription for people taking the pill. This peaked very soon after women started taking the medication, and decreased significantly for every year that they took it. In fact, women who took the pill for 7+ years were less likely to be prescribed antidepressants. There was a smaller (but still significant) increase in hospital diagnoses of depression in pill-users, and both of these effects were worse for certain types of hormonal birth control and for women in younger age groups.
Now so far this sounds interesting but also a bit flat. The study authors themselves concluded that this suggested “depression as a potential adverse effect of hormonal contraceptive use” and cautioned that more study was needed to check whether the observations that they had made were true.
But then the results were released to the media.
Now, to be fair, the study is a pretty dense read. And the mistakes that have been made about this study are widespread and common among all science reporting.
However, it’s amazing the amount of fear that you can generate when you don’t tell the whole story.
One big problem is that every article has talked about the relative risk increase from taking the pill. It sounds really scary when you are told that you are 23% more likely to get depression if you take it. But this doesn’t talk about the incidence of the disease; how many people does this actually equate to?
Using the metrics from the study, every additional prescription of antidepressants takes an extra 200–300 women on the pill. For every 5000 women who are taking the pill, there is one extra hospital diagnosis of depression. In absolute terms, the study found that the risk of getting depression that is associated with hormonal contraception was small.
Now this doesn’t mean that the information isn’t useful. From a population perspective, it might be better to fund treatments that are less likely to cause depression, or to sponsor drug companies interested in researching ways to minimize this risk. It might be worthwhile investigating the social factors that cause people to take both the contraceptive pill and antidepressants, if only to better market important treatments. For a government these results are interesting, important, and impossible to ignore.
But for an individual? For you? It doesn’t mean very much.
And that’s the central message. You can’t take results that show the effect on millions of people and insert them into your daily routine. There’s a vast gulf between a risk that you take for yourself (the pill might exacerbate your genetic predisposition towards heart disease) and a population risk (if 1 million women take the pill, a few thousand might become depressed). Whilst the risk from the pill is absolutely an issue for all women (with so few male contraceptive options, it’s unsurprising that 80% of women take the pill at some point in their lives), but it’s not something that every individual taking the pill needs to take into account.
That’s not to say that the pill definitively does or doesn’t cause depression, or even that it isn’t something you should discuss with your doctor (tip; discuss everything with your doctor, that’s what they get paid for), just that generating fear about one of the best-researched and safest methods for contraception based on this research is definitely uncalled for. The media has a responsibility to weigh risk against benefit, and in this case selling the story is almost certain to result in people opting out of safety and choosing a contraceptive method that might not be as good, or even opting out of contraception altogether. History shows that fear-mongering about medicines can cause real harm.
This is a story of a complicated knotty problem that has been distilled into a single message by news media, because “there may be a small increase in depression caused by the pill but we aren’t sure yet” is not a story that sells well.
I’m not going to give you advice on whether or not to take the pill. Not least because I have no personal experience whatsoever in the matter. But I would suggest that a news story is probably not the best place to get medical advice, and that your doctor might have a more well-informed opinion.