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At What Age Does Mental Illness Begin?

A new study investigated the age of onset for the major forms of mental illness.

Key points

  • A large-scale study investigates at what age different mental illnesses tend to start.
  • Across all mental disorders, the average age of onset was 14.5 years.
  • This shows that mental disorders start early, and early intervention can be helpful.
Source: shisu_ka/Shutterstock

Knowing at what age mental illness typically starts is highly important information for psychologists. When it is known when a disorder typically starts, early prevention measures and early interventions can be conducted at the right time. This improves the long-term well-being of the patient compared to a situation where therapy started years after the beginning of a disorder.

A New Large-Scale Study on the Onset of Mental Health Disorders

To provide robust estimates of when mental illness starts, data from as many patients as possible should be integrated. This is why Solmi and co-workers (2021) just conducted a meta-analysis of 192 studies investigating the onset of mental disorders. A meta-analysis is a statistical analysis that integrates the results of many different scientific studies. It has the advantage of having a larger sample size, increasing statistical power, and rendering the analysis less likely to be affected by characteristics of individual studies.

Overall, the 192 studies analyzed by Solmi and co-workers (2021) included data from more than 700,000 patients diagnosed with a mental disorder. Besides the age of onset for different disorders, the scientists also analyzed the percentage of people that developed a mental disorder before the age of 14, 18, and 25 years.

Mental Disorders Often Start Earlier Than Expected

When the data from all 192 studies were integrated, the authors found that the peak age of onset for mental disorders was 14.5 years. About 34.6 percent of patients showed a disorder before the age of 14, 48.4 percent before the age of 18, and 62.5 percent before the age of 25 years. This shows that for almost 50 percent of patients, mental disorders start before they reach adulthood, highlighting the importance of early intervention and prevention measures for mental health issues in adolescents.

In a second step, the scientists also analyzed the age of onset for different forms of mental disorders. In ascending peak age on onset, here is what they found:

There were no significant differences between male and female patients regarding the age of onset.

Implications of the Study

If there is one thing that the study clearly shows, it is that mental health issues in adolescents should be treated seriously. People often have the idea that most mental health conditions start in adulthood, and only developmental disorders start in childhood. When adolescents show mental issues, parents sometimes think that they will “grow out of it” or “it is just a phase.” The study shows that such ideas are wrong, and mental issues in adolescents need to be treated as in almost 50 percent of patients, mental disorders start in this life phase.

LinkedIn image: Torgado/Shutterstock. Facebook image: shisu_ka/Shutterstock


Solmi M, Radua J, Olivola M, Croce E, Soardo L, Salazar de Pablo G, Il Shin J, Kirkbride JB, Jones P, Kim JH, Kim JY, Carvalho AF, Seeman MV, Correll CU, Fusar-Poli P. (2021). Age at onset of mental disorders worldwide: large-scale meta-analysis of 192 epidemiological studies. Mol Psychiatry, in press.

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