School Peer Groups May Influence Teens’ Risk for Psychiatric Disorders

The psychiatric diagnoses of peers—as well as peers’ genetic risk for psychiatric illness—influences the mental health of adolescents, particularly in 10th through 12th grades, according to a study issued today in JAMA Psychiatry.

 

Adolescence is a period when several psychiatric illnesses emerge, but also a time when strong social networks with different peers are formed. Previous studies have found evidence supporting the social transmission of psychiatric illness, but it remains unclear how exposure to peer psychiatric disorders and their genetic predispositions compare across different disorders and different peer networks.

 

• The researchers studied 604,819 Finnish individuals with no diagnosed mental illness as of age 17 who were born between 1985 and 2000, tracking them until their first mental disorder diagnosis or through 2023. Among this group, 39% received a mental disorder diagnosis during the course of the study.
• Across all mental illnesses studied, individuals exposed during adolescence to peers with genetic risk for a mental disorder—inferred from relatives’ diagnoses—had an increased risk for the same disorder. The strongest association was for externalizing disorders (substance use or disruptive behaviors) following exposure in upper-school (grades 10 to 12) networks.
• Being exposed to peers with a psychiatric diagnosis, by contrast, was more likely to influence the subsequent development of internalizing disorders (mood, anxiety, or emotional/social functioning disorders)—with the strongest associations again seen for upper-school peer networks.

The associations were not explained by the adolescents’ own genetic predisposition or their family socioeconomic status.

 

The observed effects of peer psychiatric diagnoses or genetic predisposition were modest in magnitude, according to the researchers, who noted that they can’t rule out residual confounding due to inaccurately measured or unmeasured covariates.

 

“Taken together, our findings provide further support for peer genetic effects and social transmission of psychiatric risk in adolescence,” the researchers wrote. “Consistently stronger associations in school-based rather than geographically defined peer networks suggest that schools are a primary setting for adolescent socialization and peer influence.”

 

“Genetic Underpinnings of Peer Influence in Adolescents”

 

Jussi Alho, et al. Adolescent peers’ diagnoses and genetic predispositions and subsequent risk of mental disorders. JAMA Psychiatry. Published July 1, 2026. doi:10.1001/jamapsychiatry.2026.1752

 

(Image: Getty Images/iStock/Antonio_Diaz)