This observational study followed 19,254 unrelated females of European ancestry, born in Denmark between 1981 and 2006. Each was tracked from age 10 until her first hormonal contraception prescription or the end of follow-up, at ages up to 35. In all, 13,580 (71%) filled a prescription, and 94% of them started on the combined pill.
ADHD was not studied as a diagnosis. Researchers used gene scores for inherited tendency toward ADHD, depression, bipolar disorder and schizophrenia.
Females with a higher genetic tendency toward ADHD or depression tended to start hormonal contraception younger. The link was strongest at ages 10 to 14 and weakened with age. All four scores were linked to starting at ages 10 to 14. Only the ADHD and depression scores were linked at ages 15 to 19. None were linked to starting any type at 20 or older, but those two were linked to starting a non-oral type at ages 20 to 24. A check leaving out people with hospital-treated mental health conditions or psychiatric prescriptions found the same pattern, except for the bipolar score at ages 10 to 14.
The authors suggest that an earlier reported link between starting contraception young and depression could be partly due to shared genetics. They say the results reveal very little about why these links exist. Gene scores capture only a small part of genetic risk, and the results may not apply to other ancestries.
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The numbers Stats and what the terms mean
The statistics behind the plain-language claims above.
- Mundy, 2025: starting any hormonal contraception at ages 10 to 14, per step up in the ADHD score, HR = 1.21 [95% CI = 1.16 to 1.27], p = 6.16 × 10−18.
- Mundy, 2025: starting at ages 10 to 14, per step up in the depression score, HR = 1.21 [1.16 to 1.27], p = 1.22 × 10−17.
- Mundy, 2025: starting at ages 10 to 14, per step up in the bipolar disorder score, HR = 1.07 [1.02 to 1.13], p = 6.87 × 10−3.
- Mundy, 2025: starting at ages 10 to 14, per step up in the schizophrenia score, HR = 1.09 [1.04 to 1.14], p = 8.61 × 10−4.
- Mundy, 2025: starting at ages 15 to 19, per step up in the ADHD score, HR = 1.13 [1.11 to 1.15], p = 2.97 × 10−34.
- Mundy, 2025: starting at ages 15 to 19, per step up in the depression score, HR = 1.06 [1.04 to 1.08], p = 2.82 × 10−9.
- Mundy, 2025: starting a non-oral type at ages 20 to 24, per step up in the ADHD score, HR = 1.15 [1.08 to 1.22], p = 1.08 × 10−5.
- Mundy, 2025: starting a non-oral type at ages 20 to 24, per step up in the depression score, HR = 1.09 [1.02 to 1.16], p = 0.007.
- Mundy, 2025: the cutoff a result had to pass to count, a Bonferroni-adjusted alpha of 0.0125. What the terms mean:
- HR (hazard ratio) shows how much more likely an event is to happen at any point in time for one group than another, where 1 means no difference. Here it compares people one standard step apart on a gene score.
- 95% CI (confidence interval) is a range of values around the result that fit the data reasonably well, and a narrower range means a more precise result.
- p (p-value) shows how unusual a result would be if there were really no effect, and it depends on the study's assumptions being right. Here a result had to fall below 0.0125 to count.
- Bonferroni-adjusted alpha is a stricter cutoff than the usual one, used when several tests are run at once.
Source: Mundy J, Hall A, Agerbo E, et al.. Genetic Confounding of the Association Between Age at First Hormonal Contraception and Depression. Acta Psychiatrica Scandinavica (2025). doi:10.1111/acps.13774