The Relationship Between Cannabis Use and Schizophrenia As a Risk Factor or For Its Therapeutic Potential: A Systematic Review of Evidence

A systematic review of studies published between 2017 and 2025 found strong evidence that using cannabis with high THC content significantly raises the risk of developing schizophrenia, especially among adolescents and people with a family vulnerability. THC also worsens positive, negative, and cognitive symptoms in those already diagnosed with schizophrenia. Cannabidiol (CBD) showed antipsychotic and neuroprotective properties and therapeutic potential, but clinical evidence remains limited, with most studies being small and lacking long-term follow-up. The review argues that distinguishing between cannabis components is essential for psychiatric discussions, and large controlled trials are needed to determine CBD's therapeutic limits.

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Abstract

The rising use of cannabis in the medical field has prompted the revival of the global debate about its psychotropic effects, especially when it comes to schizophrenia, a debilitating mental disorder that afflicts approximately 20 million people around the globe. Although Δ9-tetrahydrocannabinol (THC) is commonly considered a risk factor for psychosis, cannabidiol (CBD) has been studied for its potential therapeutic use. This review aims to clarify the central controversy surrounding the question of whether cannabis worsens schizophrenia symptoms by presenting a selective analysis of the available scientific literature. A systematic review was performed according to PRISMA 2020 guidelines. PubMed, PubMed Central, Cochrane Library, and Google Scholar were searched for peer-reviewed studies published between 2017 and 2025. A total of 112 records were obtained in the first phase of the research process, and after an intense screening process, eight high-quality studies meeting the inclusion criteria were included based on rigorous quality evaluation (A MeaSurement Tool to Assess systematic Review 2 or AMSTAR 2, Cochrane Risk of Bias Tool, Newcastle-Ottawa Scale, and scale for the quality assessment of narrative review articles (SANRA)). Data were extracted and systematically synthesized across three analytical domains: THC as the cause of schizophrenia, the influence of THC on the course of symptoms, and the potential therapeutic effects of CBD. The results provided strong evidence that the risk of developing schizophrenia was significantly higher with the use of high-THC-content cannabis, particularly when used by patients with family vulnerability and by those who used cannabis regularly during adolescence. THC was also demonstrated to exacerbate not only positive and negative psychotic symptoms but also cognitive disturbances in subjects with established schizophrenia. Conversely, there was evidence for the antipsychotic and neuroprotective properties of CBD and its therapeutic potential. However, clinical evidence for CBD was still limited; most studies were small, and few had long-term follow-up. This review emphasizes the importance of distinguishing the components of cannabis in psychiatric discussions. Although THC has potent schizophrenia liability, CBD is still a novel but promising candidate for treatment. Large controlled clinical trials need to be a priority for future research to determine the therapeutic and mechanistic limits of cannabis in mental health. These implications are very important for the clinical arena, public health policy, and research agenda on the topic of cannabis use and schizophrenia treatment.