Concerns have been raised about the lack of knowledge of the benefits and harms regarding cannabis and mental health

In the UK there is strong public and political support for medical cannabis being available to patients who can benefit from it. As far back as 2016, a Populus poll found that 68% of the UK population supported the idea and last year’s change in the law to legalise medical cannabis in the UK was met with widespread political and public acclaim.

However, the fear that cannabis, even in its medical form, might be harmful still stalks much of the debate, particularly in the popular media – which makes links to mental disorders such as psychosis and schizophrenia.

Cannabis and mental health

Many health professionals are still concerned about safety which has, in part, led to the current unwillingness of NHS clinicians to prescribe the newly legalised compounds. So with many patients reporting that they consume medical cannabis to help with a wide range of health conditions, including alleviating the symptoms of mental health issues, we are in the paradoxical position that some people consume cannabis to help improve a mental health condition, whilst others view such consumption as a cause of those mental health issues, not a cure.

Media bias

Some aspects of the popular media delight in blaring out: ‘Consuming cannabis can lead to psychosis and even schizophrenia.’ Other ‘cannabis campaigners’ have an equally entrenched view that this is not the case.

The real situation is more nuanced than either of these positions. Having a debate based on such polarised views helps neither the public nor the medical professionals.

The true picture can only be ascertained by looking at evidence. For example, there is some new evidence around the effectiveness of CBD, a non-intoxicating cannabinoid found in cannabis, helping people live with schizophrenia. The randomised-control trial published in the American Journal of Psychiatry, funded by GW Research and the National Institute for Health Research showed that after six weeks of treatment, the group treated with CBD had lower levels of psychotic symptoms, and were more likely to have been rated improved and not as severely unwell by a clinician.

Limited evidence

This evidence is currently limited in scope, however, it should open the door for developing more evidence around this particular link, and also for securing evidence of efficacy or otherwise across a broader range of health issues, both physical and mental.

Stating that cannabis may contribute to symptoms of schizophrenia-like psychosis is an easy narrative because it’s been perpetuated for so long. What’s more difficult is employing rigorous science and the nuances required to have an evidence-informed discussion on this topic.


While a link exists between cannabis and psychosis, it exists mostly for people who are heavy users of THC products and who have a predisposition to psychosis. In fact, one recent study suggests that genetics could account for about 69% to 84% of the link between cannabis and psychosis. It also bears mentioning that a majority of cannabis consumers experience neither psychosis nor go on to develop schizophrenia.

Further, from self-report surveys, research shows 19% of adult cannabis users were daily or near-daily users – i.e., those at the highest risk. This means that a majority of individuals who use cannabis are not doing so in ways that would potentially put them at risk for these commonly discussed, severe health issues.  The frequency of use of THC, and starting cannabis at a younger age, are also important risk factors for developing psychosis.

Framing the narrative

The narrative around psychosis and cannabis often ignores the importance of the varying social and structural factors that we know shape health outcomes. These factors have been essentially disregarded in this wider conversation around risk – things such as poverty or childhood trauma and abuse – many of which also increase levels of stress, a known risk factor for psychosis.

Unless the pressure to stigmatise cannabis is resisted and, by implication, cannabis-based medicines, and champion the role of solid evidence-based analysis we risk allowing the development of medical cannabis to be stunted.

That would be a tragedy for the potential patients and a failure on the part of the body medical, civic and political to explore all options that can help improve quality of life.

Dr. Caroline MacCallum
Clinical instructor in the Department of Medicine at UBC
Medical director at Greenleaf Medical Clinic

Dr. Jenna Valleriani
CEO National Institute for Cannabis Health and EducationExecutive
Director Hope for Health Canada

Dr. Caroline MacCallum is an internal medicine specialist with expertise in complex pain and cannabis, a clinical instructor in the Department of Medicine at UBC, and medical director at Greenleaf Medical Clinic. Jenna Valleriani is the CEO of the National Institute for Cannabis Health and Education, and executive director of Hope for Health Canada.

Dr. MacCallum will be presenting at Medical Cannabis: What UK Doctors Need to Know being hosted by Sapphire Medical Clinics on the 29th October in London.

A version of this opinion editorial was originally published in the Globe and Mail.

See full article on Health Europa