Mental disorders are often considered a type of non-infectious disease. Non-infectious/communicable diseases include cardiovascular diseases, diabetes, cancer, chronic respiratory diseases, as well as mental and neurological disorders. Most of these illnesses have a genetic background that manifests when environmental risk factors coexist, such as obesity, tobacco use, or alcohol consumption.

But could mental health disorders be, in a sense, contagious? An interesting study in Finland recently found that adolescents who have classmates with mental illness have a higher chance of developing mental disorders in adulthood. The study was performed between 1985 and 1997, involving a total of 713,809 cohort members with a median age of 16.1 years.

More than 47,000 adolescents involved in the study had already received a mental disorder diagnosis by the ninth grade. The remaining members were followed up until a diagnosis of mental disorder, emigration, or death up to 2019. The exposure variable was defined as having one or more classmates diagnosed with a mental disorder in the same school class in the ninth grade.

The main outcome was the occurrence of mental disorders during follow-up. The results showed that having classmates with a mental disorder diagnosis in the ninth grade was associated with a later risk of being diagnosed with a mental disorder........

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