Alcohol and other substance use problems are common among individuals with schizophrenia. Many of the previous studies have focused on clinical comorbidity, not on longitudinal studies aiming to look for possible causal associations. We aimed to investigate if premorbid or early substance use predicts long-term clinical and social course in schizophrenia.

A systematic review to identify potentially relevant studies was conducted. Only studies with a follow-up period of at least two years were included. We studied following outcomes: negative, positive and total symptoms, clinical remission, hospitalizations, social functioning, employment, and global outcome.

The search identified 9343 unique potentially relevant articles of which 20 studies presenting results from 24 samples met our inclusion criteria. The meta-analysis included 5 to 13 studies in each outcome category. The studied in outcome groups were mainly moderate to high heterogeneous. In meta-analysis, substance use associated modestly with outcome, all the associations (Spearman's r) were non-significant and between −0.05 and 0.10. Non-significant findings are explained by the fact that the original studies found often opposite results, indicating both worse and better long-term outcome for early substance users.

Although comorbid substance use associates with poorer outcome in schizophrenia, the early substance use has only a modest effect as a predictor of long-term outcome. This difference between these two designs may be explained for instance with poorer treatment adherence of dual diagnosed patients.

Alcohol and other substance use problems are common among individuals with schizophrenia.

Many of the previous studies have focused on clinical comorbidity, not on longitudinal design.

The aim of this study was to investigate if premorbid or early substance use predicts long-term clinical and social course in schizophrenia.

A systematic review to identify potentially relevant studies was conducted. Studies with a follow-up period of at least two years were included. Following outcomes were studied: negative, positive and total symptoms, clinical remission, hospitalizations, social functioning, employment, and global outcome. Spearman's correlations were used to summarize results, negative correlations indicating poorer outcome with substance use.

The search identified 10776 unique potentially relevant articles of which 25 studies met our inclusion criteria. The meta-analysis included 5 to 13 studies in each outcome category. Moderate to high heterogeneity was found between studies in each outcome group. In meta-analysis, substance use associated modestly with outcome. All the associations were non-significant and correlations between −0.06 and 0.09. Non-significant findings are explained by the fact that the original studies found often opposite results, indicating both worse and better long-term outcome for early substance users.

Although comorbid substance use associates with poorer outcome in schizophrenia, the early substance use has only a modest effect on long-term outcome. This difference to studies on current comorbidity may indicate that those who continue substance abuse have poor outcome, e.g. due to poor treatment adherence, whereas those who stop the abuse may have relatively good outcome.

Low IQ is a risk factor for psychosis, but the effect of high IQ is more controversial. The aim was to explore the association of childhood school success with prodromal symptoms in adolescence and psychoses in adulthood.

In the general population-based Northern Finland Birth Cohort 1986 (n = 8 229), we studied the relationship between teacher-assessed learning deficits, special talents and general school success at age 8 years and both prodromal symptoms (PROD-screen) at age 15–16 years and the occurrence of psychoses by age 30 years.

More prodromal symptoms were experienced by those talented in oral presentation [boys: adjusted odds ratio (OR) 1.49; 95% confidence interval 1.14–1.96; girls: 1.23; 1.00–1.52] or drawing (boys: 1.44; 1.10–1.87). Conversely, being talented in athletics decreased the probability of psychotic-like symptoms (boys: OR 0.72; 0.58–0.90). School success below average predicted less prodromal symptoms with boys (OR 0.68; 0.48–0.97), whereas above-average success predicted more prodromal symptoms with girls (OR 1.22; 1.03–1.44). The occurrence of psychoses was not affected. Learning deficits did not associate with prodromal symptoms or psychoses.

Learning deficits in childhood did not increase the risk of prodromal symptoms in adolescence or later psychosis in this large birth cohort. Learning deficits are not always associated with increased risk of psychosis, which might be due to, e.g. special support given in schools. The higher prevalence of prodromal symptoms in talented children may reflect a different kind of relationship of school success with prodromal symptoms compared to full psychoses.