Effects of Common Mental Disorders on Personality Over a 17-Year Period

While personality is generally considered stable, it may be influenced by common mental disorders (CMDs). In a large population sample of 55,056 individuals, we investigated the associations of CMDs, recorded in a national registry over 17 years, with self- and informant-rated Big Five personality traits. Besides comparing diagnosed and undiagnosed people, we considered the number and timing of anxiety, depressive, and alcohol use disorder diagnoses that people had accumulated over 17 years. Those diagnosed with a CMD during the study period differed from undiagnosed people by about 0.50 SDs higher neuroticism and slightly higher openness. For neuroticism, however, the difference from undiagnosed people was larger among those diagnosed more recently and on more numerous occasions, whereas the association did not depend on the number or timing of diagnoses for openness. These findings are consistent with heightened neuroticism in response to mental health issues which may take over a decade to gradually return to the baseline, and less open people being less likely to seek help for mental health issues. We also found evidence consistent with extraversion and conscientiousness temporarily lowering in response to depressive disorder. These findings were consistent across self- and informant-ratings, suggesting they were not artefacts of measurement bias. This study, the largest to date, finds that personality changes in response to mental disorders could persist for at least a decade, much longer than previously thought. Keywords: Big Five personality; personality trait change; psychiatric traits; longitudinal