In addition, OC use in adolescence has been tied to an increased risk for depression later in life. However, some experts believe the study’s methodology may be flawed.
The investigators tracked more than 250,000 women from birth to menopause, gathering information about their use of combined contraceptive pills (progesterone and estrogen), the timing of the initial depression diagnosis, and the onset of depressive symptoms that were not formally diagnosed.
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Women who began using these OCs before or at the age of 20 experienced a 130% higher incidence of depressive symptoms, whereas adult users saw a 92% increase. But the higher occurrence of depression tended to decline after the first 2 years of use, except in teenagers, who maintained an increased incidence of depression even after discontinuation.
This effect remained, even after analysis of potential familial confounding.
“Our findings suggest that the use of OCs, particularly during the first 2 years, increases the risk of depression. Additionally, OC use during adolescence might increase the risk of depression later in life,” Therese Johansson, of the department of immunology, genetics, and pathology, Science for Life Laboratory, Uppsala (Sweden) University, and colleagues wrote.
The study was published online in Epidemiology and Psychiatric Sciences.
Inconsistent findings
Previous studies suggest an association between adolescent use of hormonal contraceptives (HCs) and increased depression risk, but it’s “less clear” whether these effects are similar in adults, the authors wrote. Randomized clinical trials have “shown little or no effect” of HCs on mood. However, most of these studies didn’t consider previous use of HC.
The researchers wanted to estimate the incidence rate of depression associated with first initiation of OC use as well as the lifetime risk associated with use.
They studied 264,557 female participants in the UK Biobank (aged 37-71 years), collecting data from questionnaires, interviews, physical health measures, biological samples, imaging, and linked health records.
Most participants taking OCs had initiated use during the 1970s/early 1980s when second-generation OCs were predominantly used, consisting of levonorgestrel and ethinyl estradiol.
The researchers conducted a secondary outcome analysis on women who completed the UK Biobank Mental Health Questionnaire (MHQ) to evaluate depressive symptoms.
They estimated the associated risk for depression within 2 years after starting OCs in all women, as well as in groups stratified by age at initiation: before age 20 (adolescents) and age 20 and older (adults). In addition, the investigators estimated the lifetime risk for depression.
Time-dependent analysis compared the effect of OC use at initiation to the effect during the remaining years of use in recent and previous users.
They analyzed a subcohort of female siblings, utilizing “inference about causation from examination of familial confounding,” defined by the authors as a “regression-based approach for determining causality through the use of paired observational data collected from related individuals.”
Adolescents at highest risk
Of the participants, 80.6% had used OCs at some point.
The first 2 years of use were associated with a higher rate of depression among users, compared with never-users (hazard ration, 1.79; 95% confidence interval, 1.63-1.96). Although the risk became less pronounced after that, ever-use was still associated with increased lifetime risk for depression (HR, 1.05; 95% CI, 1.01-1.09).
Adolescents and adult OC users both experienced higher rates of depression during the first 2 years, with a more marked effect in adolescents than in adults (HR, 1.95; 95% CI, 1.64-2.32; and HR, 1.74; 95% CI, 1.54-1.95, respectively).
Previous users of OCs had a higher lifetime risk for depression, compared with never-users (HR, 1.05; 95% CI, 1.01-1.09).
Of the subcohort of women who completed the MHQ (n = 82,232), about half reported experiencing at least one of the core depressive symptoms.
OC initiation was associated with an increased risk for depressive symptoms during the first 2 years in ever- versus never-users (HR, 2.00; 95% CI, 1.91-2.10).
Those who began using OCs during adolescence had a dramatically higher rate of depressive symptoms, compared with never-users (HR, 2.30; 95% CI, 2.11-2.51), as did adult initiators (HR, 1.92; 95% CI, 2.11-2.51).
In the analysis of 7,354 first-degree sister pairs, 81% had initiated OCs. A sibling’s OC use was positively associated with a depression diagnosis, and the cosibling’s OC use was also associated with the sibling’s depression diagnosis. “These results support the hypothesis of a causal relationship between OC use and depression, such that OC use increases the risk of depression,” the authors wrote.
The main limitation is the potential for recall bias in the self-reported data, and that the UK Biobank sample consists of a healthier population than the overall U.K. population, which “hampers the generalizability” of the findings, the authors stated.