Background: The study aimed to review recent literature not included in previous reviews and ascertain the correlation between early marijuana use among adolescents, between 12 and 18 years of age, and the development of schizophrenia in early adulthood. A further aim was to determine if the frequency of use of marijuana demonstrated any significant effect on the risk of developing schizophrenia in early adulthood.
Methods: Five hundred and ninety-one studies were examined; six longitudinal cohort studies were analyzed using a series of nonparametric tests and meta-analysis.
Results: Nonparametric tests, Friedman tests, and Wilcoxon signed tests showed a highly statistically significant difference in odds ratios for schizophrenia between both high- and low-cannabis users and no-cannabis users.
Conclusion: Both high- and low-frequency marijuana usage were associated with a significantly increased risk of schizophrenia. The frequency of use among high- and low-frequency users is similar in both, demonstrating statistically significant increased risk in developing schizophrenia.
Keywords: longitudinal studies; mental health.
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