A longitudinal study of twins in Sweden found that adolescents who reported being bullied at age 15 were more likely to develop symptoms of obsessive-compulsive disorder (OCD) later in life (between ages 18 and 24). However, this association was observed only in dizygotic twins and disappeared in monozygotic twins, suggesting that the link is likely due to shared genetic factors rather than bullying being a direct cause of the disorder. The findings were published in Molecular Psychiatry.
Obsessive-compulsive disorder is a mental health condition characterized by persistent, unwanted thoughts (obsessions) and repetitive behaviors or mental rituals (compulsions) performed to reduce anxiety. Common obsessions include fears of contamination, harming others, or needing things to be symmetrical or feel “just right.”
Compulsions often involve excessive cleaning, checking, counting, or repeating actions. These behaviors can be time-consuming and disruptive, interfering with daily life, relationships, and work. OCD affects about 1–2% of the population and typically begins in adolescence or early adulthood. Treatment usually involves a combination of cognitive-behavioral therapy—particularly exposure and response prevention—and medications such as selective serotonin reuptake inhibitors (SSRIs).
Study author Josep Pol-Fuster and his colleagues aimed to investigate the longitudinal link between OCD and bullying victimization. Specifically, they sought to determine whether being bullied at an earlier age could lead to the development of OCD.
To explore this question, the researchers linked data from the Swedish National Patient Register (which provides diagnostic information) with data from the Child and Adolescent Twin Study in Sweden, an ongoing project focusing on mental and physical health in all twins born in Sweden from July 1, 1992, onward.
The analysis included data from 16,030 twins born between 1993 and 2006. Of these, 6,863 were complete twin pairs, and 2,304 were incomplete. A total of 139 twins—approximately 0.9% of the sample—were diagnosed with OCD. Among those with OCD, 63% were girls, compared to 55% among those without the diagnosis.
At age 15, participants completed the Revised Olweus Bully/Victim Questionnaire to assess bullying victimization. OCD symptoms were assessed at ages 18 and 24 using the Brief Obsessive-Compulsive Scale and the Obsessive-Compulsive Inventory – Revised. In addition, researchers extracted the first recorded OCD diagnoses from the National Patient Register.
The results showed that individuals diagnosed with OCD were more likely to report having been bullied at age 15 compared to their peers without OCD (11% vs. 4%). They were also more likely to have been diagnosed with anxiety disorders (6.5% vs. 0.5%) or depressive disorders (7% vs. 0.7%).
However, when the researchers analyzed the data separately for dizygotic and monozygotic twins, they found that the association between bullying and OCD was present only in dizygotic twins and absent in monozygotic twins. Monozygotic twins develop from a single fertilized egg and share 100% of their genes, while dizygotic twins develop from two separate eggs and share about 50% of their genes—similar to regular siblings. This finding suggests that shared genetic factors likely contribute to both the risk of being bullied and the development of OCD.
Because of this, although bullying victimization and OCD appear to be linked, the relationship is more likely to be driven by genetic confounding than by a direct causal effect of bullying.
“These results suggest that the association between bullying victimization and OCD/OCS [obsessive-compulsive disorder / obsessive-compulsive symptoms] is likely due to genetic confounding and therefore incompatible with a strong causal effect. Other mechanisms, such as evocative gene-environment correlations, are more plausible explanations for the observed associations,” the study authors concluded.
The study sheds light on the nature of the link between OCD and bullying victimization. However, it should be noted that bullying victimization was assessed through self-reports leaving room for reporting bias to have affected the results.
The paper, “Association between bullying victimization and obsessive compulsive disorder: a population-based, genetically informative study,” was authored by Josep Pol-Fuster, Lorena Fernández de la Cruz, Kayoko Isomura, Anna Sidorchuk, Ralf Kuja-Halkola, Paul Lichtenstein, Brian M. D’Onofrio, Isabell Brikell, Henrik Larsson, Elles de Schipper, Jan C. Beucke, and David Mataix-Cols.