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Getting the balance right: a conversation about cannabis and psychosis

Three experts unpick what we really know – and what we don’t.



The relationship between cannabis and psychosis - and its portrayal in the media - has fuelled debate and perpetuated stigma.

The relationship between cannabis and psychosis is a long-publicised and polarised topic. At this year’s Cannabis Europa, three experts sat down to unpick what we really know – and, crucially, what we don’t. 

For decades the relationship between cannabis and psychosis – and its portrayal in the media – has fuelled debate and arguably, perpetuated stigma.

While some argue that a causal association between cannabis use and psychosis has been identified in psychiatric epidemiology among a minority of users, others say that factors such as poverty, social deprivation and trauma make it difficult to infer a causal link with any certainty. 

Now that increasing numbers of people around the world have legal access to cannabis for both medicinal and recreational use, where does that leave us?   

At this year’s Cannabis Europa in London, one of the world’s leading researchers in the field of cannabis and psychosis, Dr Marta Di Forti, sat down with psychiatrists and UK cannabis clinicians, Dr Niraj Singh, of Lenus Global and Dr Luisa Searle, associate medical director of Jorja Emerson Centres, to discuss what we know about the relationship between cannabis and psychosis.  

 This is what we learned… 

 Firstly, what is psychosis and how common is it? 

Psychosis is a broad term which can cover multiple things. 

“It’s very important to be aware when we talk about psychosis, we’re not always talking about the same thing,” said Dr Singh. 

“It’s a very broad spectrum.” 

It is most often associated with  psychotic illnesses and delusional disorders, but in some cases it can also be the result of complex trauma, severe anxiety, and/or use of alcohol, amphetamines, cocaine and various other drugs.  

The prevalence of psychosis varies across the world, depending on the different risk factors which include genetics, social deprivation, ethnicity, unemployment, loneliness, trauma and obstetric complications

It can generally be categorised by a change in perception, thinking and belief that affects an individual’s level of functioning and/or alienation from the wider community. It can also impact cognition and executive function, such as our attention span and the ability to plan and execute tasks. 

Dr Searle thinks about psychosis in two ways: A detachment from reality, which is when delusions and cognitive symptoms come into play, and a disorder of salience. Salience is related to the importance or significance that we attach to certain events, for example something which a healthy person may dismiss, becomes very prominent and important to someone experiencing a psychotic episode.  

Before we get into the details, let’s clear up the differences between prescribed and ‘street’ or illicit cannabis… 

 There are a number of key differences between cannabis that is now prescribed legally in the UK and illicit cannabis that has generally been used in research studies. 

 Products which are prescribed for medicinal use must comply with Good Manufacturing Processes (EU GMP), and be accompanied by certificates of analysis. As a result doctors and patients usually have a better understanding of what’s in the product in terms of cannabinoid and terpene content and ratios.  

“With medicinal cannabis, there is an accountability there,” said Dr Searle.  

There are processes, legislation and safety standards which manufacturers must adhere to. Medical cannabis is produced under stricter conditions and there are regulations around what types of pesticides you can use to make them safe for human consumption. 

“The levels of THC and CBD are also much better controlled and often much lower than that which we find on the street, which can have very high percentages of THC up to 25% and above and which is often not suitable for the majority of patients. It can also lack CBD, which is a very important component of the plant and can help balance and offset some of the side effects from unopposed THC.” 

Dr Niraj Singh and Dr Luisa Searle discuss the relationship between cannabis and psychosis. Photo: Cannabis Europa.

Is it ever okay to prescribe cannabis to someone with psychosis? 

Generally clinicians are advised to avoid prescribing cannabis to anyone with a personal or family history of psychosis. However, in the appropriate circumstances and under careful clinical guidance it can actually be used as a tool to help manage symptoms.  

In her clinic, which is the first in the UK to treat patients with cannabis-induced psychosis, Dr di Forti prescribes the licensed cannabis-based drug Sativex to those who want to reduce their reliance on illicit cannabis, under a ‘harm reduction approach’.  

“My work has come from [studying] the side-effects, but that doesn’t mean I don’t acknowledge that compounds like THC and CBD that modulate the endocannabinoid system can be used for medicinal purposes,” said Dr di Forti.  

“The people I see in my clinic have been heavy cannabis users who have developed a dependence and want to make changes. With Sativex, I know exactly how much THC or CBD [they are taking] but also I know that they are the only ones present…. We are just beginning to scratch the surface in knowing the effects of the other 144 cannabinoids, both beneficial and potentially harmful.” 

According to Dr Singh prescribed cannabis can also be beneficial in cases of trauma-induced psychosis, when accompanied by symptoms such as severe anxiety, flashbacks and intrusive thoughts. 

“It’s important we do all the relevant background checks and understand the aetiology before we prescribe to any patient,” he said. 

“In some cases, psychosis can be linked with severe anxiety or complex trauma… as well as having flashbacks and intrusive thoughts people can get psychotic as well. Medicinal cannabis can be really beneficial and I’ve seen some really good outcomes, but obviously, we need to be mindful of potential risks and explain the potential side-effects.” 

Dr Searle added: “If somebody has a family history, I would like to see them on a case-by-case basis and this is where the importance of having a clinician involved in cannabis prescribing comes into play. I’m here to have those conversations with patients about the risks and benefits and talk them through it, educate them and allow them to make informed decisions. They don’t have that opportunity on the black market.” 

Often patients with trauma-induced psychosis will turn to cannabis to ameliorate their symptoms, but Dr di Forti notes that studies have shown their outcomes actually worsened, both clinically and functionally, compared to those who have stopped consumption or reduced their frequency of use. 

What about someone with a diagnosis of schizophrenia? 

Some studies have begun to explore the potential of CBD as a treatment for psychosis in patients with schizophrenia. A study from 2021 found that CBD-cigarettes had an ‘antipsychotic medication sparing effect’, when used as an adjunctive treatment for acute psychosis.

Meanwhile, an ongoing study at the University of Oxford in the UK is examining the potential of CBD as a treatment for psychosis and psychotic symptoms. According to Dr di Forti, while CBD has been found to be relatively safe in terms of not exacerbating psychotic symptoms, the ‘verdict is still out’ on whether it could be a potential ‘cure’. 

From a clinical point of view, Dr Singh argues that in some cases, depending on the patient, there could be an argument to prescribe CBD for patients with a diagnosis of schizophrenia. 

“It’s about having that compassion and understanding of what’s led up to that point,” he said. 

“In the future I think there could be a place to offer treatment to people with schizophrenia, where appropriate.”

Dr Niraj Singh. Photo: Cannabis Europa

Do we need to think about reducing the risk of harm when prescribing cannabis? 

In the UK, any clinician on the GMC specialist register can prescribe medicinal cannabis. But Dr di Forti would like to see more psychiatrists involved in the prescribing process, even when it is being prescribed for a non-psychiatric condition.  

“If neurologists are prescribing cannabis for multiple sclerosis or a physician is prescribing it for pain and they’re expecting people to take it on a daily basis, as most of these conditions require, I would like to see psychiatrists more involved,” she said. 

“Monitoring the onset of psychosis is not like asking somebody if they have developed an upset stomach, it’s a very subtle subtle process that you need to have the instruments to detect.” 

Have rates of psychosis increased in recent years, as cannabis has become more readily available to many? 

Research shows that illicit cannabis is now more potent, containing higher levels of THC, than it was two decades ago. Access to legal cannabis is also increasing across the globe, so have rates of psychosis increased alongside this? 

“In South London, which is the catchment area where I work, we have seen a rise in psychosis, and there is an analysis ongoing to see if this has any relationship to the changes in cannabis,” said Dr di Forti.

“There have also been changes in the context of the catchment area, which includes variation in other risk factors… we have an analysis ongoing that shows that cannabis use in the context of social deprivation might have a very different effect on mental health than using cannabis in a middle class background.”

A number of studies examining rates of psychosis have produced mixed results. Dr di Forti pointed to research from Denmark which found over the last decade an increase in the number of psychosis cases attributed to cannabis, after controlling for social demographics and other substance misuse. 

Meanwhile, a recent paper from the US found no ‘statistically significant difference’ in the rates of psychosis-related diagnoses, or prescribed antipsychotics, in states with medical or recreational cannabis policies compared to those where it is still prohibited.  

Dr Singh and Dr Searle also noted that from a clinical point of view they haven’t noticed an increase in the number of patients seeking help for psychosis in recent years. But establishing the cause of psychosis is a complex and challenging area for researchers in the field.

“Certainly in the substance misuse world, I’ve not noticed increased rates of psychosis,” said Dr Searle.  

 “It is rare that you will see somebody who just uses cannabis and so that interplay between the other substances that they use, high levels of trauma present in substance misusers, high levels of deprivation, and homelessness as well, all interplay into contributing to psychosis. It’s a real challenge for researchers to pick apart what causality is behind the psychosis that we’re seeing out in the community.” 

Dr Marta di Forti. Photo: Cannabis Europa

How can we understand more about who might be at risk of cannabis-induced psychosis? 

 Dr di Forti recently secured £2.5million in funding from the Medical Research Council for the Cannabis and Me study, which aims to recruit 6,000 cannabis consumers to explore a range of environmental and biological factors behind the different effects people experience. 

 The study is open to all cannabis consumers, whether they are prescribed it, self-medicate or consume recreationally – unless they have a clinical diagnosis of psychosis – and will use a combination of virtual reality, psychological and cognitive analysis, DNA testing and epigenetics in its analysis.  

“I only see the negative effects, so for me to be able to work even more effectively with the population I serve as a clinician, I need to have a 360 degree picture,” said Dr di Forti. 

“It’s really important to understand the difference between this group and what keeps people well despite the use of cannabis on a daily basis and the people I see in my clinic.  

“We shouldn’t forget when we use cannabis, whatever the reason, it interacts with the endocannabinoid system and it might be that the way the individual endocannabinoid system responds and interacts with cannabis might also modulates the breath for their response and the degree of side-effects they experience.” 

The study currently has 2,300 people enrolled but Dr di Forti is urging more consumers to come forward to help her collect experiences from a range of socioeconomic backgrounds. 

“Currently 75% of the sample are white Caucasian, there is nothing wrong with this, but it doesn’t represent London and the breadth of cannabis users,” she added.

“I need all the ethnic groups, all the social demographics. Otherwise when we are analysing people, we might end with data that does not represent all of the experiences.”

Find out more about the study here 

And moving forward, what would you like to see change to restore balance in this discussion?

The majority, if not all, of the research that has been done in this field to date has been on those using illicit cannabis. Meanwhile, the negative portrayal of cannabis in the media has not only made doctors reluctant to prescribe, but prevented open and collaborative discussion about the potential risks and benefits of cannabis. So how do we overcome this?

The key is collaboration and education, all three agree. 

“The data from epidemiological studies needs to be complementary to the experience of prescribing cannabis. We need to move away from this polarised debate where the bad guys talk about cannabis and psychosis, and the good guys say cannabis can be used as a medicine, because I think any sensible psychiatrist will accept both sides,” said Dr di Forti.

“In medical school, we still don’t teach students about the endocannabinoid system. How can medical students have any idea about the good and bad of cannabis without knowing about the target system in human physiology?” 

 Dr Singh added: “No medicine is perfect and it’s not a panacea at all, but we do need to redress the balance of the narrative. That starts in schools and in medical schools, where the message currently is that cannabis causes extreme damage to physical and mental health. Information and education is really important.

Dr Searle agreed: “The only way we’re going to move forward in the industry is through education. Through the constant banging of the drums about [the importance of] having a balanced view.

“Yes, there are risks and there are benefits and somewhere in between might be right for you.” 

The Relationship Between Cannabis and Psychosis panel was hosted by Cannabis Health editor, Sarah Sinclair, as part of The Greenhouse Sessions at Cannabis Europa from 2-3 May, 2023. Follow the Cannabis Europa Youtube channel for more content from the event. 

This article was reviewed for accuracy by Dr Marta di Forti, Dr Niraj Singh and Dr Luisa Searle. 

Home » Health » Getting the balance right: a conversation about cannabis and psychosis

Sarah Sinclair is a respected cannabis journalist writing on subjects related to science, medicine, research, health and wellness. She is managing editor of Cannabis Health, the UK’s leading title covering medical cannabis and CBD, and sister titles, Cannabis Wealth and Psychedelic Health. Sarah has an NCTJ journalism qualification and an MA in Journalism from the University of Sunderland. Sarah has over six years experience working on newspapers, magazines and digital-first titles, the last two of which have been in the cannabis sector. She has also completed training through the Medical Cannabis Clinicians Society securing a certificate in Medical Cannabis Explained. She is a member of PLEA’s (Patient-Led Engagement for Access) advisory board, has hosted several webinars on cannabis and women's health and has moderated at industry events such as Cannabis Europa. Sarah Sinclair is the editor of Cannabis Health. Got a story? Email / Follow us on Twitter: @CannabisHNews / Instagram: @cannabishealthmag


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