1 Institute of Psychiatry, Psychology & Neuroscience King's College London London UK.
2 Department of Psychiatry McGill University & Douglas Mental Health University Institute Montreal Quebec Canada.
3 School of Criminology & the Research Center of the Montreal Mental Health University Institute University of Montreal Montreal Quebec Canada.
4 School of Public Health University of Montreal Montreal Quebec Canada.
5 Department of Pediatrics and Psychology University of Montreal Montreal Quebec Canada.
6 Department of Psychology Concordia University Montreal Quebec Canada.
7 Department of Epidemiology, Biostatistics, and Occupational Health, School of Population and Global Health McGill University Montreal Quebec Canada.
8 Danish Research Institute for Suicide Prevention Mental Health Centre Copenhagen Copenhagen Denmark.
9 School of Psychology Laval University Quebec City Quebec Canada.

Background: Victimisation has been associated with self-harm (with or without suicidal intent), but little is known about this association during young adulthood-a distinct developmental period. Further, not all individuals who experience victimisation will later engage in self-harm, suggesting the influence of other factors. The present study examined whether perceived victimisation is associated with self-harm during young adulthood while adjusting for confounders such as peer victimisation and mental health difficulties in adolescence. Additionally, we investigated whether genetic susceptibility for mental health difficulties moderates this association.

Methods: Participants were from the Quebec Longitudinal Study of Child Development (1998-2023); a population-based birth cohort from the Canadian province of Quebec, with victimisation and self-harm measures in young adulthood (sample 1; N = 1235), and who provided blood samples and had been genotyped (sample 2; N = 552). At 20 years old, they were asked how often they had experienced forms of victimisations in the past 12 months (e.g., insulted you, put you down in front of others) without specifying the perpetrator. At 20-25 years old, participants reported self-harm. Polygenic scores (PGSs) for depression, attention deficit hyperactivity disorder (ADHD) and suicide attempt were calculated.

Results: Overall, 17.2% (sample 1) participants reported self-harm at age 20-25 years. Victimisation was associated with self-harm (OR = 1.66, 95% CI = 1.45, 1.89, for each standard deviation increase in victimisation), even after adjusting for confounders, for example, victimisation and mental health in adolescence (OR = 1.53, 95% CI = 1.26, 1.86). In sample 2, PGSs for depression and suicide attempt (not ADHD) were associated with self-harm as well as victimisation in young adulthood, and none moderated the association between victimisation and self-harm.

Conclusion: Regardless of genetic susceptibility indexed by PGSs, young adult exposed to victimisation are at higher risk of self-harm. Continuing efforts to prevent victimisation beyond childhood/adolescence and into young adulthood may contribute to reducing self-harm risk.