In this article, we review a recent meta-analysis study (statistically combining the results of all available studies) on the potential effects of cannabidiol (CBD) for schizophrenia.
Schizophrenia is a serious mental health disorder in which individuals experience repeated episodes of hallucinations (such as hearing voices), delusions, paranoia, and strong feelings of depression and social withdrawal. The condition affects around 0.3 to 0.7% of all adults, usually in late adolescence or as a young adult.
Doctors typically treat schizophrenia with antipsychotic drugs. However, these drugs carry a range of unwanted adverse side-effects including muscle tremors, sleepiness, sexual dysfunction, and weight gain. In addition, a significant number of patients do not achieve an adequate reduction in symptoms using these drugs.
As taking CBD is relatively safe and well-tolerated, patients and doctors alike have been interested in it as a potential alternative to antipsychotic drugs for schizophrenia.
The widespread interest in CBD’s medicinal properties is leading to a growing body of research investigating its impact on many health conditions. The antipsychotic properties of medicinal cannabinoids in general (but not necessarily for CBD in particular) have led to several reviews of their effects on schizophrenia. One study showed that cannabinoids might act in a similar manner to the antipsychotic drug aripiprazole, by the partial activation of dopamine receptors. However, to date, the majority of studies have proven inconclusive.
The study that we are reporting on in this post, however, looked specifically at the properties of CBD for schizophrenia compared to placebo and other antipsychotic drugs, taken alone and in combination. The researchers included only high-quality trials for consideration.
Although we do not know how CBD works as an antipsychotic, we do know that it works differently from other cannabinoids and THC. CBD has a different mechanism of action that does not operate via dopamine or cannabinoid receptors. Therefore, CBD for schizophrenia could represent a new class of antipsychotic treatments. Experts suggest that CBD may avoid dopamine receptor-induced adverse side effects. Furthermore, CBD could also be used alongside existing treatments.
There were to important initial findings of the meta-analysis. First, there were only three high-quality published studies examining the effectiveness of CBD as an antipsychotic treatment for schizophrenia. Second, it was not possible to verify the source or quality of the CBD oil used in each clinical trial.
The final findings related to efficacy are the following:
Two later studies noted that adding CBD oil to stable antipsychotic treatments also enhanced positive symptoms compared to a placebo. However, CBD add-on therapy did not improve the effectiveness of the overall treatment or reduce negative symptoms and side effects. Thus, the comparison of using one drug plus CBD oil as an add-on produced conflicting results. In conclusion, the addition of CBD oil did not show any significant difference compared to adding a placebo.
There were some issues which may explain these conflicting outcomes, however. For example, the patients in the monotherapy investigative group were younger and had worse baseline symptoms and acute untreated schizophrenia. In comparison, those in the therapy plus added CBD oil investigative group had already been receiving treatment for 4 weeks. Therefore, their symptoms may already have improved before the addition of CBD to their therapy regimen, leaving no room for noticeable improvement.
The lack of available high-quality research on CBD for schizophrenia ultimately limited the possibility to draw firm conclusions on CBD’s comparative effectiveness. However, the researchers did not include some of the trials because they thought the research procedures were not rigorous enough.
For example, in a case report in 2006, the addition of CBD oil to antipsychotic drug treatment reduced psychotic symptoms in a schizophrenia patient who had been resistant to treatment up to that point. A later study by the same researcher, however, found only mild or no improvements when given to three further patients. As such, taking these excluded studies into consideration, indications remain that CBD have potential positive benefits for schizophrenia. However, this needs scientific confirmation.
In summary, the studies that the scientists reviewed provided insufficient evidence on the efficacy of using CBD for schizophrenia. More in-depth research with more types of patients and over longer time periods are necessary. At present, four new clinical trials are underway to answer some of these questions.
Kopelli E, Samara M, Siargkas A, Goulas A, Papazisis G, Chourdakis M. The role of cannabidiol oil in schizophrenia treatment. A systematic review and meta-analysis. Psychiatry Res. 2020 Sep;291:113246. doi: 10.1016/j.psychres.2020.113246. Epub 2020 Jun 22. PMID: 32599446.