Relationship between the duration of methamphetamine use and psychotic symptoms: A two-year prospective cohort study.

BACKGROUND: Psychosis is a key harm associated with methamphetamine (MA) use. This study examined the relationship between the duration of MA use and risk of psychotic symptoms. METHODS: A cohort of 528 individuals with chronic MA use was followed for two years after leaving treatment center in Guangdong, China. Psychotic symptoms were assessed using the Positive and Negative Syndrome Scale at baseline and four follow-up visits (6, 12, 18 and 24 months after baseline). MA use during the past six months was investigated at each assessment. Generalized Estimating Equations for longitudinal panel data were developed to examine the risk of MA-associated psychotic symptoms among individuals with different durations of MA use. 340 MA users who completed at least one follow-up were included in the analysis. RESULTS: During 6-month intervals, participants who reported MA use showed a two-fold increase in the risk of psychotic symptoms compared to those with no MA use (odds ratio [OR] = 2.15, 95% confidence interval [CI] = 1.33-3.49). A dose-response effect was found between the duration of MA use and the risk of psychotic symptoms (continued 12-month MA use vs. no use: OR = 2.84, 95% CI = 1.39-5.77; continued 18-month MA use vs. no use: OR = 9.93, 95% CI = 3.58-27.57). There was no assessment for 24-month intervals due to a small sample size of the continuous use group. CONCLUSIONS: Longer periods of MA use predicted a higher risk of experiencing psychotic symptoms. Early prevention of MA use could help reduce the risk of psychosis in MA users.