The trajectory of two negative symptom dimensions in first-episode psychosis and the role of cannabis use: A 10-year follow-up study

Objective: To investigate the trajectories of diminished expression and apathy over 10 years, and to explore the effects of baseline and persistent cannabis use on these trajectories while controlling for other potential sources and predictors of secondary negative symptoms. Methods: 351 participants with a first episode of non-affective psychosis were examined at baseline and invited to follow-up at one year and 10 years. Trajectories of diminished expression and apathy were investigated using linear mixed models. Cannabis use and potential predictors of secondary negative symptoms were then added to assess their impact. Results: Both diminished expression and apathy decreased during follow-up, with the most improvement between baseline and 1 year. Cannabis use at baseline was associated with a long-lasting higher symptom load for diminished expression, but not apathy. Including persistent cannabis use further strengthened the association with diminished expression. Conclusion: Both baseline and persistent cannabis use after a first episode of psychosis were associated with more severe diminished expression. The results imply a causal relationship between cannabis use and diminished expression and suggest that measures to reduce cannabis use before and after psychosis onset may reduce expressive negative symptoms.

Henrik Myhre Ihler, Siv Hege Lyngstad, Erlend Strand Gardsjord, Line Hustad Widing, Camilla Bärthel Flaaten, Gina Åsbø, Kristin Fjelnseth Wold, Magnus Johan Engen, Carmen Simonsen, Torill Ueland, Vik Lagerberg, Ingrid Melle, Kristin Lie Romm