A recent article in The Guardian claims that "The pill is linked to depression – and doctors can no longer ignore it". It does so on the basis of a new study published in JAMA Psychiatry, which tracked all women aged 15-34 in Denmark over a number of years, and measured (among other things) their use of oral contraceptives, and their use of anti-depressants. The study's headline results were that:
a) women who used oral contraceptives had a 23% higher risk of using anti-depressants for the first time
b) adolescent females who used oral contraceptives had an 80% higher risk of using anti-depressants for the first time
The author of the Guardian article seems to regard these results as highly alarming. Yet there are several reasons not to be too consternated.
First, from what I can tell, the JAMA Psych study was largely correlational, rather than causal: only age and year were controlled for in the main analyses. Second, the authors also measured women's diagnoses of depression, and––for that outcome––the increase in risk associated with oral contraceptive use was only ~10% for women overall (but it was still around 70% for adolescents). Third, and most importantly, the effect sizes do not appear to be very large.
The crude incidence rate for women overall was ~1.7 per 100 person years. In other words, if 100 women who were not using oral contraceptives lived for 1 year, 1.7 of them would be expected to use anti-depressants for the first time during that year. The results above imply that this figure rises to 2.1 for women using oral contraceptives. The crude incidence rate for adolescents was ~0.9 per 100 person years. So if 100 adolescents who were not using oral contraceptives lived for 1 year, 0.9 of them would be expected to use anti-depressants for the first time during that year. The results above imply that this figure rises to 1.7 for adolescents using oral contraceptives. (The crude incidence rates for diagnoses of depression were much lower.)