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Dr Marta Di Forti – cannabis, psychosis and what you need to know about £2.5m study

Dr Di Forti explains the motivations behind a new study hoping to explore the effects of cannabis on the brain.



Dr Marta di Forti - cannabis, psychosis and what you need to know about £2.5m study
Dr Marta Di Forti is lead researcher on King’s College London’s Cannabis & Me study

A major new UK study is hoping to better understand the effects of cannabis on the brain, lead researcher Dr Marta Di Forti explains what it hopes to achieve – and addresses criticism over her previous work.

The Medical Research Council (MRC) has allocated over £2.5 million of funding to Cannabis & Me, a scientific study into the effects of cannabis on the human brain.

King’s College London is aiming to recruit 6,000 participants who are either using cannabis or have never used it, in order to explore a range of environmental and biological factors behind the different effects people experience.

Those who consume will be asked to share their experiences with cannabis – both positive and negative – to help better understand why some suffer from adverse effects and others do not.

It is thought this will be the largest independent study to use a combination of virtual reality, psychological and cognitive analysis, DNA testing and epigenetics in its analysis. 

However, some cannabis campaigners have advised caution around the study, with lead researcher, Dr Marta Di Forti often thought of as “anti-cannabis” based on some of her previous work. 

Dr Marta di Forti - cannabis, psychosis and what you need to know about £2.5m study

Dr Marta Di Forti

Dr Di Forti is a prominent researcher in the field of cannabis and psychosis. She has published several papers on the subject, largely exploring links between high potency cannabis and risk of psychotic episodes, many of which have been picked up by mainstream media outlets. 

She also runs the UK’s only Cannabis Clinic for Patients with Psychosis.

In the Cannabis & Me study, however, Dr Di Forti says she is keen to hear from a wide cohort of consumers, particularly those who experience health and wellbeing benefits or enjoyment from the plant.

We spoke to Dr di Forti to find out more about the motivations behind the research. 

CH: Can you tell us a bit more about what you are hoping to achieve with the Cannabis & Me study?

Dr Di Forti: My hope is to be able to reach out to a sample of people that really represent those who are using cannabis. As a clinician and a psychiatrist, I tend to see people who use cannabis, and at the same time are suffering from psychosis, so I have had a view of the issue which is focused on the small minority. 

What I don’t see are those that are using cannabis for medicinal or even recreational reasons and only getting benefits or pleasure. This is the exact group of people I am reaching out to, because I would like to understand how that experience is different from the group I know. 

In a world where cannabis is becoming more popular for different reasons, including the debate around medical cannabis being more widely available, I want to see if the data can help us to understand who the minority are that do experience adverse effects, and how we can keep them safe. The debate on cannabis has always been so polarised. I would really like to bridge these two sets of experiences, so that those using it can feel safe and confident to do so, and those who are prescribing can monitor it safely. 

CH: Some cannabis consumers have been reluctant to get involved, and may – based on your previous work – hold a view that you are ‘anti-cannabis’, what would you say to those people?

Dr Di Forti: First of all, I would say that I’m one of the few clinicians using their own funding to prescribe products which contain cannabis. I prescribe Sativex, off-licence, to my young patients who have a psychotic disorder and are heavily dependent on cannabis to help them reduce their reliance on street cannabis. I think that if you can use well- controlled medicinal cannabis compounds to give people a chance to feel better, then why not? 

The reason that my voice has always been associated with a voice against cannabis, is because my duty is towards the people I see that do come to harm. Even if they are a minority, it is a minority that deserves to be represented. I also need to understand why they come to harm and everybody else doesn’t. It is the conversation with the [other group] that I’m interested in. How is it different from your experience? What are you doing differently in terms of your cannabis use? How are you different biologically from the people I see, that means you are able to experience the benefits? 

We know in medicine that the response to any drug – and when I say drug I put everything together, including cannabis and prescribed medication – can vary significantly from person to person. I am the first one to accept that there will be people who come to no harm, but I don’t know enough about them.

If the people who are having a different experience are not prepared to share it with me and the scientific community, we’re just going to keep adding to a polarised debate. 

CH: What are the specific effects that you are interested in finding out about?

Dr Di Forti: In the questionnaires and face to face assessment we will ask about the whole spectrum of effects. However, as I am a psychiatrist, not an immunologist, the focus of my research is not to look at the effects on the immune system or the effect on inflammation or pain, because that is not what I know about. The main focus is on the psychological response. I can use my expertise to tease out who experiences psychological side effects and how my understanding of neuroscience and neurophysiology can, with the data that we aim to collect, tease out the population at risk.

The point of my research is to find a way to identify these people, and look after them properly, then everything else can be done in a much more open, safer way, hopefully with more clinicians engaging and feeling comfortable to prescribe.

I’m preoccupied with psychosis, because that’s all I know. But that’s not to say that cannabis is all about psychosis, if anything it’s a small part of the story, but is a part of the story that can have an impact on a few people, and these are the people I have a responsibility to. The questions I’m trying to answer actually come from my patients, they don’t come from me.

CH: A lot of your previous research has focused on linking cannabis and psychosis, what is your professional view as a clinician?

Dr Di Forti: The population that I see are people who have a family history of psychosis, and in these people you can sense that cannabis is pushing them over a threshold, which is already higher than the general population. But you cannot say that cannabis is the only risk factor for their psychosis. Psychosis is not a uni-factorial disorder, as many risk factors are usually added together. 

The reason why it is important that people who have a family history do know about cannabis and psychosis is because for them it is certainly safer to stay away from it. But again, I can’t even tell you that everybody who has a family history, if they use cannabis, will develop psychosis because we don’t know that. This is exactly something that I want to find out in my study.

CH: And what have you seen among the patients in your clinic? 

Dr Di Forti: There are two settings in which I treat patients with cannabis and psychosis. One is the Cannabis Clinic for Patients with Psychosis, which is a new service and I’m also a clinician in an early intervention service, which is one of the busiest in the country. We have under our care at any given time, between 240 and 300 patients at the beginning of psychosis and 45-50 per cent have come to the first stage of psychosis from cannabis. I’m not saying that for all of them cannabis is the main factor, because they come from a history of trauma, as well poverty, migration and other complications – there are a pool of risk factors. But certainly when they are able to reduce [their cannabis use] or they change the way they use it, or for those who want to, stop completely, you do see a significant improvement.

I do see people who use cannabis twice and have a very acute psychotic reaction, even if they don’t have any family history. And then they stop and the psychosis never comes back. I also see people who use cannabis for a decade before they develop psychosis to a level that needs immediate psychiatric attention.

What my interaction with my patients is teaching me is that it’s not all or nothing, there is so much in between that we still need to understand. If we understand more about that and how you can get to a threshold where you can still get the benefits without the side effects, we can give people more access to safe use. 

CH: It could be said that the way your work has been portrayed in the media and elsewhere, has contributed to the societal stigma around cannabis. Would you agree? And is this a fair representation?

Dr Di Forti: I understand that journalists have to write headlines and get people to click on them. Sometimes the political debate about cannabis has used my data in a context which doesn’t necessarily represent my view, and this is what tends to upset me. People now associate me with the idea that nobody should use cannabis and that cannabis is a toxic substance, which is not what I think. 

There’s no reason why even acknowledging that cannabis might cause adverse effects in some people equates to the fact that nobody should use it. This is not the way I function in my everyday practice. I hope that when people reach out to me, they can understand that I do not have a polarised view. Even in my clinical practice I don’t tell people what to do regarding their cannabis use, but I work with them towards finding what might be beneficial. 

Cannabis is so present in my clinical work that I hope I can contribute my experience, my knowledge and the resources I have, including the MRC fund, in reaching a middle ground between the demonising approach that the media has had – using my data as well – and the extreme other narrative saying that cannabis can only benefit and is a cure for everything. I think this would be useful for anybody who’s using cannabis or thinking about it, first of all for medical reasons, but also why not for a safe recreational approach. I hope I do not come across as a prohibitionist dinosaur, because this is not what I am. 

CH: Can you tell us a bit about what will be involved in the study for those who decide to take part?

Dr Di Forti: The starting point is a 30-40 minute online questionnaire, followed by a face to face assessment to go into more detail of the cannabis experience and life history, such as previous trauma. Then there is a virtual reality experience, which can be used to measure in real-time, people’s reaction to circumstances and the variation in perception and psychological response. 

Then there is the biological aspect. Genetics can give us very important information. We will ask people for a blood sample to look at the DNA structure. Within this analysis, we’ll be looking at the genes which we know are involved in the metabolism of THC and CBD, as well as the other cannabis compounds, to see if there might be variation in the response in terms of how people metabolise it. 

At the same time we will measure the endocannabinoid system, by looking at blood levels of anandamide and 2-Ag. We do wonder if the reason why people have different effects is also related to the biological interaction between our endocannabinoid system and the cannabinoids that come from the plant. 

CH: You will also look at epigenetics as part of the study, can you explain why this is important?

Dr Di Forti: We know that DNA has a role in shaping our interaction with the environment, but it’s not just our DNA structure that defines how we respond to a substance or to an environmental exposure, it’s also the other way around. Our DNA can be switched on and off, depending on our environmental exposure. We know that diet, for instance, has an important role in where and when the DNA is expressed to protein and therefore linked to biological effects. 

When we compare people who are using cannabis and we look at the amount of THC and CBD they have in the blood, the DNA structure and the response of the endocannabinoid system, we might find that in people who experience beneficial effects the DNA is switched on and off in a different way compared to those who develop psychological distress.

CH: How can people find out more?

Dr Di Forti: I am happy for people to contact me via email if they have any questions or concerns about the study. I am open to any discussion as long as they are happy to engage in a polite and open conversation. It is only when people say that because it’s a plant, nobody can come to any harm from it, that I get a bit suspicious. 

You can contact Dr di Forti at: 

More information about the study is available at

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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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