A recent study published in BMC Psychiatry reviewed clinical studies relating to the use of medicinal cannabis in the treatment of psychiatric disorders.


Cannabis and its extracts (CBD & THC) have a broad range of medical applications. This has been increasingly explored as a result of the rapidly changing global legislation concerning cannabis legality.

Although the potential for cannabis to treat a litany of medical conditions has begun to be investigated, there is little information about its usefulness within a psychiatric context.

The Study

This study sought to clarify the existing evidence about the use of medical cannabis in the treatment of common psychiatric disorders. Researchers analyzed all available studies that had investigated the clinical use of cannabis within a psychiatric context. They then consolidated this data and presented it in a systematic-review format.


Authors analyzed scientific literature on human subjects that involved both whole cannabis as well as cannabis-isolate derivatives in the treatment of psychiatric disorders and mental illness symptoms. Researchers used electronic medical databases to find appropriate papers. All relevant studies published up until July 2019 were selected for analysis.

The authors decided to focus on literature that strictly entailed clinically-oriented studies regarding the use of cannabis-based treatments (CBD & THC) for the symptoms of psychiatric disorders in this review. A total of 481 studies were identified as being potentially relevant but upon further review, only 13 were selected as being fit for final analysis.



Two of the most common forms of anxiety disorders are Generalised Anxiety Disorder and Social Anxiety Disorder.

Those who suffer from Social Anxiety Disorder, as the name suggests, experience anxiety within social settings. In contrast, those with Generalized Anxiety Disorder will experience continual anxiety throughout the day. The review noted that there were no studies that had investigated the use of medicinal cannabis in the treatment of Generalized Anxiety Disorder.

However, one study had assessed the potential of CBD to treat Social Anxiety Disorder. This used a simulated public speaking test in order to analyze two groups of participants: those who had been diagnosed with Social Anxiety Disorder, and those who did not have an anxiety-related diagnosis, i.e. “healthy” participants.

Each group of participants received either an oral dose of CBD or a placebo before the test. Results showed that those who had been treated with CBD displayed significant reductions in anxiety, mental impairment, and discomfort during the exam. It was also noted that participants treated with CBD had significant reductions in anticipatory anxiety in the period before the speaking test.

Post-Traumatic Stress Disorder (PTSD)

Many individuals who have experienced a traumatic event will suffer from PTSD. This includes even those who have not been directly involved but have been a witness. This review included two studies that used medical cannabis to treat PTSD patients. One used CBD in a capsule form and reported an overall decrease in PTSD-related symptoms in 28% of participants.

Another study used traditional cannabis flower and found more than a 75% reduction in PTSD-related symptoms in participants.


Authors of this review were unable to find any studies that had investigated the use of cannabis in people with depression alone (i.e. as a “primary” condition not due to the secondary effect of another disorder (i.e. “secondary depression”). However, they were able to locate four that included findings on the effect of cannabis on secondary depression induced by disorders such as multiple sclerosis and cancer. All of these studies used nabiximol, a natural cannabis extract containing standardized levels of THC, CBD, and terpene.

Three of these studies (1, 2, 3) reported no significant effect on secondary depression arising from the diagnosis of multiple sclerosis and cannabis withdrawal. The fourth study involved depression as a secondary outcome of cancer. The findings showed a significant decrease in mood for those who used the highest dose of nabiximol, compared to those patients who did not.

This data was viewed as being congruent with existing evidence suggesting links between heavy cannabis use and higher levels of depressive symptoms, compared with those who use cannabis lightly or not at all.


Bearing certain similarities to anxiety, depression, and other mood disorders, insomnia often arises as the result of a pre-existing condition. This includes conditions that induce physical or mental discomfort that can predispose individuals to a poor night’s rest.

The review included a case study of a 10-year old girl who had experienced early childhood trauma. After being given oral CBD oil during a clinical trial, a decrease in anxiety was found along with an improvement in sleep.

Another study involved 72 adults who had been provided with CBD for anxiety and sleep complaints. https://www.ncbi.nlm.nih.gov/pubmed/30624194 Findings showed a 79% reduction in anxiety scores (as assessed by the “Hamilton Anxiety Rating Scale”) over 3 months. Results also showed an improvement in sleep quality (as assessed by the “Pittsburgh Sleep Quality Index”) for 67% of participants. However, this improvement occurred in the first month but did not continue for the remainder of the study.


There is ample evidence within scientific literature that suggests that cannabis can cause schizophrenia. For example, there tends to be an earlier onset of schizophrenia and psychosis in cannabis users of younger age. https://www.fullspectrum.com/cannabis-and-youth-onset-psychosis/ Most studies suggest THC is the primary psychoactive constituent of cannabis responsible, at least in part, for the increased risk of developing schizophrenia or psychosis. Many have also postulated that CBD, a non-psychoactive constituent of the cannabis flower, may function as a proverbial buffer in mitigating the psychoactive and potentially harmful effects of THC.

The concept of CBD having a potentially opposing effect on THC has spearheaded several studies in this review. All of these investigated the use of CBD within a medical setting to treat the symptoms of schizophrenia.

One study found that a set dose of CBD administered for approximately one month was beneficial for patients with treatment-resistant schizophrenia.

Another study compared the use of CBD to an antipsychotic medication typically used in the treatment of schizophrenia. Findings showed that CBD resulted in a significant clinical improvement in comparison to the antipsychotic medication. Additionally, it was noted that patients who were treated with CBD suffered fewer severe side-effects as compared to those treated with the antipsychotic.

A third study of similar nature, in which CBD was compared to an antipsychotic medication, yielded similar findings. Schizophrenic patients treated with CBD were found to have lower levels of psychotic symptoms when compared to those who were treated with the antipsychotic medication. Those patients who were treated with CBD were also demonstrated to have a greater likelihood of being rated as improved according to standardized clinician ratings.

However, the final study within this category did not provide beneficial findings of CBD use compared to a placebo in the treatment of schizophrenia. It is worth noting that those who were given CBD were observed to have greater levels of sedation compared to those who took a placebo.

Bipolar Disorder

The review noted that there have been no clinical trials, to date, that have assessed the utility of cannabinoids in the treatment of bipolar disorder. The paper did, however, highlight a case study in which two patients with Bipolar Disorder were given CBD as part of their treatment. The first showed improvement in bipolar symptoms when given a combination of CBD and medication for bipolar disorder. However, there was no improvement noted with CBD treatment alone. The second patient experienced no improvement in symptoms at all during the study.


Only one study was located regarding the use of nabiximol in the treatment of adults with ADHD. https://www.ncbi.nlm.nih.gov/pubmed/28576350 This study found that while nabiximol did not increase cognitive performance, it did not impair cognition either. Findings also suggested a potential, albeit small, correlation between nabiximol use and the improvement of hyperactive and impulsive symptoms associated with ADHD.

Significance, Limitations & Final Thoughts

Although the data available to the authors of this systematic review was lacking, the evidence discussed here may contribute to improved patient treatment in the future. Several of the studies featured were not properly analyzed for statistical significance, placing their findings on precarious ground. Others involved so few participants and were of such an isolated nature in regards to any similar studies corroborating them, that their findings must be taken with a grain of salt.

To provide patients alternative, potentially superior, forms of treatment, further work needs to be conducted following the studies included in this review. In conducting a comprehensive analysis, despite their limitations, this review provides a valuable framework that can be built upon. It provides a concise picture of the current evidence, and researchers will undoubtedly be motivated to add to the gaps in the data. In doing so, the evidence base will become stronger, more conclusive, and clinically-relevant.

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