Frequency of methamphetamine use impact on vulnerability to persistent psychosis: a four years long cohort in Haiphong

Background
Methamphetamine (MA) use is growing worldwide. People who use MA have poorer mental and epidemiological research on the use of MA and mental health outcomes are needed. Our objective was to describe long-term psychotic outcomes in a cohort of people who use MA, and to examine the impact of frequency of use on psychotic disorder.
 
Methods
Using respondent driven sampling survey conducted between 2019 and 2023 among people who inject drugs in Haiphong Vietnam (Drive Mind study), we constituted a cohort of people with a current regular MA use at baseline to study frequency of use impact on lasting vulnerability to persistent psychosis. 
We recorded six visits in total. MA use was assessed by urine tests and self-report. Structured interviews were conducted to cover socio-demographic characteristics, drug use, quality of life and other health-related outcomes. Psychotic symptoms were screened using the Mini International Neuropsychiatric Interview (5.0.0). Psychiatric diagnosis was then confirmed by a psychiatrist. 
 
Results
We included in a prospective cohort study 106 participants with current regular MA use at baseline in 2019. 60% of the MA users had a current psychotic disorder at baseline. 
We found an important difference in MA use between subjects with and without current psychotic disorder at baseline (respectively 16 and 8 times per month); and a difference in MA use between subjects with at least one acute psychotic disorder vs subjects without any acute psychotic disorder within the 4 years (respectively 10 and 8 times per month).
We also found an important difference in MA use between subjects with MA related vs non-related psychotic disorder (respectively 7 and 5 times per month).
Finally, we found an important difference in MA use between subjects with transient vs sustained psychotic disorder (respectively 6 and 8 times per month).
In this analysis, due to the size of our sample, we could not achieve statistically significant effect. 
 
Conclusions
An important part of the people with regular MA use will develop psychotic symptoms and frequency of MA use seems to have an important impact on the risk to have a sustained psychotic disorder. Larger population samples will be needed in order to better understand frequency of MA use impact on acute psychotic disorder versus a lasting vulnerability to mental disorders.