A small clinic in south London is confronting a growing mental health emergency. The Cannabis Clinic for Patients with Psychosis represents the only facility in the UK—possibly anywhere—to offer specialist dual-diagnosis support for adults managing high-potency cannabis psychosis.

Based in Denmark Hill, the clinic provides integrated care for people with psychosis who are attempting to reduce their cannabis use. That it stands alone in tackling these interconnected issues seems remarkable given the established links between them.

A 2019 study by King’s College London, published in the Lancet Psychiatry, estimated that 12% of new psychosis cases across 11 European locations were linked to high-potency cannabis use. In London, where high-potency strains dominate the market, the figure reached 30%.

Devastating Stories Behind High-Potency Cannabis Psychosis

Isiah, now 29, first tried marijuana at 14. He became a daily user by 17. At university, studying event management during the pandemic, he smoked more “because this is how you meet people.” But he developed growing “feelings of suspiciousness”—first towards his housemates, then towards his workmates.

He struggled to sleep, “started to isolate,” and cannabis became a coping mechanism. Smoking three joints daily, he felt he could trust no one.

Two years ago, Isiah found himself on the roof of a south London shopping centre, about to jump. “I was very done,” he recalls. “It felt there was no other route or option.” He was exhausted by paranoia that had grown in tandem with his cannabis habit.

An employee reached him “in the nick of time.” Despite receiving therapy and medication, he still uses cannabis daily. No service has supported him in tackling his addiction—until the Cannabis Clinic.

Katie, 46, grew up in care. She was only eight when she first tried cannabis. She became a daily user at 12. “I was self-medicating with it for many years,” she explains.

She heard voices from a young age. “They’re very intrusive, commanding voices that usually tell me to harm myself or other people.” Smoking about 20 joints daily by age 20, she was first admitted to hospital after “running down the Old Kent Road wearing fluffy pyjamas and nothing on my feet at 2am thinking I was God.”

Over two decades, she was sectioned 50 times. Despite medication and support, none targeted her cannabis use. A year after finding the clinic, she is now abstinent.

Rising Incidence of High-Potency Cannabis Psychosis

At University Hospital Lewisham, consultant Diego Quattrone runs the psychiatric intensive care unit. He reports that at least 80% of new admissions involve cannabis use.

He feels the dangers are overlooked. Cannabis use is “among the strongest factors associated with violence before and during admission.” Meanwhile, “daily use of high-potency cannabis” is associated with “a distinct subtype of violence driven by psychotic symptoms, such as paranoid delusions and hallucinations.”

A study in the Lancet Psychiatry in 2019 found south London had the highest incidence of psychosis in Europe. It identified cannabis as a contributor.

Sir Robin Murray, a professor of psychiatric research at King’s College London, describes the situation starkly. “I think we are at the beginnings of an epidemic.” He compares it to when diabetes experts warned about fast food obesity in the 1980s. “As cannabis becomes more available, more potent, then we’re going to see more, more and more psychosis.”

High-Potency Cannabis Dominates Market

The high potency of modern cannabis proves crucial to understanding psychosis rates linked to skunk-type strains. Forty years ago, dried leaf marijuana found in Britain commonly contained 3% THC. In London, skunk-like cannabis of an average 14-16% THC now accounts for 94% of the street market.

Dr Marta Di Forti, the clinic’s clinical lead and professor of drug use, genetics and psychosis at King’s, explains the challenge. “My patients will tell you they can’t get hold of low-potency cannabis even if they wanted to.”

Cannabis use is declining in England and Wales, according to the Office for National Statistics. In London it is falling sharply—only 6.8% of 16- to 59-year-olds had used the drug in 2023-24, compared with 14% in 2001-02.

However, Di Forti explains, those who do use are doing so more frequently. She points to a large study called Cannabis and Me, led by King’s and published in BMJ Mental Health in August. This questioned 3,389 former and current cannabis users aged over 18. “Fifty per cent were daily users and the overall consumption of cannabis per week was 17 joints.”

Innovative Approach to Treating High-Potency Cannabis Psychosis

The clinic takes just 16 people at a time. It offers them weekly one-to-one meetings for up to a year, lively weekly online support sessions, and monthly brunch groups. Currently, 14 people sit on the waiting list. They are welcome at brunches and receive regular reassuring telephone calls.

It was the sheer persistence of Dr Di Forti that brought the clinic into being. First came a trial by the Maudsley Charity, then a commission from the South London and Maudsley NHS foundation trust. She is its clinical lead. With two part-time practitioners, she has helped 90 people since the NHS commission.

Of those who completed the clinic’s intervention, 74% have stopped using cannabis. Of that group, 91% have returned to education or work.

Di Forti is devastated that people now wait months for vital one-to-one sessions. Is the wait dangerous? “Of course,” she says. “It is a huge wasted opportunity. The chances of them getting a severe presentation of their psychosis and needing hospital admission is between three and four times greater.”

Practical Support for Complex Symptoms

Service users create “cravings boxes” filled with items to distract them when needed. This apparently lighthearted task exemplifies the clinic’s stance of tackling practical withdrawal hurdles alongside psychological issues.

Senior practitioner Jodie Lynn explains other approaches. “Sometimes we do role-play: how to have difficult conversations. Some people find it really difficult to set boundaries with their peers. And there are cannabis diaries: we get people to record when they’re having joints, how they were feeling before and afterwards—the triggers.”

Sleep and dreaming emerge as an important area. Heavy cannabis users typically never dream. When dreams return as they withdraw, they can be terrifying. “It’s just about supporting them through that,” says Lynn.

Many users hear voices—often derogatory—harbour “grandiose beliefs” about their spirituality, powers, even celebrity, and experience visual hallucinations. One-to-one sessions can be online to work around these complexities. “We’re working with people who might be a bit paranoid about coming out of the house,” says Lynn.

Individual Experiences of High-Potency Cannabis Psychosis

Aaron, 23, started smoking at 18 at university. The habit became three joints daily. He describes his psychosis as “dissociation from reality,” “a disregard, like apathy.” This resulted in erratic behaviour leading to arrest. “I was loud in public, shouting, running from police.” He was admitted to hospital twice. It is two weeks since he last used.

Kenneth, 31, observes everything intently. His psychosis is dominated by sounds, which often seem to come from inanimate objects. From age 22 he used every day. Now it’s “once or twice” a month. He was using to “socialise, experiment.” To cope? “Without realising it,” he says. “I didn’t think much about why until I came to the clinic.” Making connections is central here.

Barriers to Recovery

Isiah’s mother, Nicci, 53, sits close to him, her eyes revealing how drained she is. Isiah lives at home. She recalls his distressed calls from university. Later, he would tell her that his workmates “were in contact with each other, trying to harm him.”

He had once been a fun-loving teenager keen to take up acting. “I just didn’t recognise my son,” she says. “There were moments he could only just about trust me.”

Both financially and emotionally, his habit haunts them. “He has to come off it,” she says. “Because it’s like the king. It’s ruling everything. It’s there every day.”

Isiah has been on the clinic’s waiting list for two months. Despite being taken to hospital after his suicide attempt, receiving therapy and medication, he remains unable to stop using cannabis.

Lower-Level Paranoia Also Rising

Professor Murray cites an increase in lower-level paranoia too. “Those who are using a lot are more likely to be a bit paranoid. They’re not sufficiently paranoid to get admitted, but they’re sufficiently paranoid to quarrel with colleagues, to be suspicious of friends, to fight with their spouse.”

Decreased perception of harm is one potential reason for increased consumption, driven partly by increased use of cannabis for medicinal purposes. While the NHS prescribes for a small number of conditions, some private clinics prescribe much more freely.

“‘If cannabis is medicinal it can’t be too bad’: this is something I get all the time from my patients,” says Di Forti.

Transformative Results Show Way Forward

Katie’s transformation demonstrates the clinic’s power to change lives. She still hears voices “pinging off in my head” but can live well. “My paranoia was so bad I couldn’t get on a bus or a train, could barely get out of bed and leave my house at my worst. Now I’m here and everywhere,” she says. She is sleeping and eating again.

Hers is a seismic transformation. Implemented widely, the clinic’s integrated approach could stem a tide of cannabis-induced psychosis cases. “I wouldn’t say I’m better, but I’m a lot healthier—I’m able to do a lot more,” she says.

The clinic can feel like a tiny bastion against a rising threat. Yet its success rate—74% of completers stopping cannabis use—demonstrates that specialized dual-diagnosis support works.

With only one such facility in the entire UK, and 14 people currently waiting months for treatment, the question becomes urgent: how many more lives could be saved if this model were replicated nationwide?

Source: dbrecoveryresources