Isiah stood on a shopping centre rooftop in November 2023, convinced there was no other way out. Katie heard voices commanding her to harm herself and others. Aaron found himself shouting in the streets, running from police. All three share something in common: severe mental health damage from today’s ultra-potent cannabis strains.

On a crisp Sunday morning at a small clinic in Denmark Hill, south London, nine young people sit around tables laden with jelly sweets, fidget toys and colouring books. They’re creating “cravings boxes”: personal collections of items to distract them when the urge to smoke becomes overwhelming. This unassuming gathering represents the front line of a battle most Britons don’t realise is being fought.

The Cannabis Clinic for Patients with Psychosis is the only facility in the UK, possibly anywhere, offering specialist support for adults battling both psychosis and cannabis dependency simultaneously. That it stands alone in tackling these intertwined conditions seems extraordinary, given what research now reveals about the links between them.

The Numbers Tell a Chilling Story

A 2019 King’s College London study published in the Lancet Psychiatry estimated that 12% of new psychosis cases across 11 European locations were linked to super-strength cannabis use. In London, where ultra-potent varieties dominate the market, that figure jumped to 30%.

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. The drug’s dangers are consistently overlooked, he argues, noting that use ranks “amongst the strongest factors associated with violence before and during admission.”

Daily consumption of ultra-potent cannabis, Quattrone explains, correlates with “a distinct subtype of violence driven by psychotic symptoms, such as paranoid delusions and hallucinations.”

When Dreams Become Nightmares

Twenty-nine-year-old Isiah first tried marijuana at 14, becoming a daily user by 17. During university, studying event management through the pandemic, he smoked more “because this is how you meet people.” But something darker was taking root.

“I remember growing feelings of suspiciousness,” he recalls, seated beside his exhausted mother Nicci at the clinic’s monthly brunch group. “First towards my housemates, then to my workmates at a part-time office job.”

Unable to sleep, increasingly isolated, Isiah turned to cannabis to cope. Soon he was smoking three joints daily, trusting no one. The paranoia grew until that November night when he climbed onto the Lewisham shopping centre roof, having first walked past every place important to him: primary school, secondary, college.

“I remember my head was telling me: ‘You’re probably better off doing this,'” he says.

An employee reached him in the nick of time. Yet despite hospital treatment, therapy and medication, Isiah still uses cannabis daily. He’s been waiting two months for one-to-one sessions at the clinic, the only service offering to tackle his addiction alongside his mental health condition.

His mother Nicci, 53, sits close during our conversation, eyes revealing her exhaustion. “He has to come off it,” she says quietly. “Because it’s like the king. It’s ruling everything.”

The Potency Problem Nobody’s Discussing

Forty years ago, dried marijuana found in Britain typically contained 3% THC (tetrahydrocannabinol, the compound producing the “high”). Today, skunk-like varieties averaging 14-16% THC account for 94% of London’s street market.

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

The clinic defines super-strength cannabis as anything containing 10% or more THC. By that measure, virtually everything available on London streets qualifies. These ultra-potent strains pose far greater dangers than the marijuana of previous generations.

Cannabis consumption overall is declining in England and Wales, according to Office for National Statistics data. In London, usage dropped from 14% of 16-59-year-olds in 2001-02 to just 6.8% in 2023-24.

However, Di Forti identifies a troubling pattern: those who do use are consuming far more frequently. A large study called Cannabis and Me, led by King’s and published in BMJ Mental Health, questioned 3,389 former and current cannabis users. Half were daily users, with overall consumption averaging 17 joints weekly.

“I Thought I Was God”

Katie, now 46, grew up in care and first tried cannabis aged eight. By 12, she was using daily. “I was self-medicating for many years,” she explains.

She heard voices from a young age: intrusive, commanding voices telling her to harm herself or attack others. By 20, smoking roughly 20 joints daily, she was first admitted to hospital.

“I was running down the Old Kent Road wearing fluffy pyjamas and nothing on my feet at 2am thinking I was God,” she recalls.

Over the following two decades, Katie was sectioned 50 times under the Mental Health Act. Despite receiving medication and support, none addressed her cannabis dependency directly. The two problems, psychosis and addiction, were treated as separate issues.

A year after finding the Cannabis Clinic, Katie is now abstinent. She still hears voices “pinging off in my head,” but can manage them. Her paranoia was previously so severe she couldn’t board a bus or train, could barely leave her bed. Now she’s sleeping and eating properly again.

“I wouldn’t say I’m better, but I’m a lot healthier. I’m able to do a lot more,” she says, representing the seismic transformation possible when both conditions are tackled together.

A Clinic Fighting Against the Tide

The Cannabis Clinic operates with just two part-time practitioners alongside Di Forti. It accommodates 16 people simultaneously, mostly men in their twenties, offering weekly one-to-one meetings for up to a year, lively online support sessions, and monthly brunch groups. A further 14 people currently languish on the waiting list.

Since receiving its NHS commission from South London and Maudsley NHS Foundation Trust, the clinic has helped 90 people. Of those completing the intervention, 74% stopped using cannabis. Of that group, 91% returned to education or employment.

Di Forti is devastated by the waiting times. Is it 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.”

The clinic’s approach tackles practical withdrawal hurdles alongside psychological issues, with minimal pressure. Senior practitioner Jodie Lynn describes role-playing exercises for difficult conversations, cannabis diaries tracking triggers and feelings, and support through the terrifying dreams that often return when heavy users stop.

“We’re working with people who might be a bit paranoid about coming out of the house,” Lynn explains. One-to-one sessions can be conducted online to accommodate these complexities.

The Epidemic Nobody’s Acknowledging

Sir Robin Murray, professor of psychiatric research at King’s College London (and Di Forti’s husband. “It does dominate our dog walks,” she admits), describes the situation starkly: “I think we’re at the beginnings of an epidemic.”

He compares it to diabetes experts “banging on” about fast food obesity in the 1980s. “We thought, ‘They’re just exaggerating’, and it turned out to be true. As cannabis becomes more available, more potent, then we’re going to see more, more and more psychosis.”

Murray cites an increase in lower-level paranoia that doesn’t result in hospital admission but manifests in quarrels with colleagues, suspicion of friends, fights with spouses. The ripple effects of super-strength cannabis extend far beyond psychiatric wards.

Twenty-three-year-old Aaron, manipulating a black fidget toy during the brunch group, started smoking at 18 at university. The habit grew to three joints daily. His psychosis manifested as “dissociation from reality,” an “apathy” producing erratic behaviour that led to arrest.

“I was loud in public, shouting, running from police,” he recalls. He was admitted to hospital twice. It’s been two weeks since he last used.

Kenneth, 31, well-spoken and observant, experiences psychosis dominated by sounds seemingly emanating from inanimate objects. From age 22 he used daily; now it’s once or twice monthly. “I didn’t think much about why until I came to the clinic,” he says. “Making connections is central here.”

The Medicinal Cannabis Paradox

Decreased perception of harm is driving increased consumption, Di Forti argues, partly fuelled by growing medicinal cannabis use. Whilst the NHS prescribes for a small number of conditions, some private clinics prescribe far more liberally.

“‘If cannabis is medicinal it can’t be too bad’: this is something I get all the time from my patients,” she explains. Yet the dangers of ultra-potent cannabis remain regardless of how it’s obtained or why it’s used.

The clinic represents a tiny bastion against a rising threat. Yet 20 minutes with Katie demonstrates its power to transform lives. Implemented widely, this integrated approach could stem a tide threatening to overwhelm mental health services.

South London had the highest incidence of psychosis in Europe according to a 2019 Lancet Psychiatry study, which identified cannabis as a significant contributor. This part of the capital has a reputation for cannabis consumption, but the true story concerns not the number of users but the extraordinary potency of what they’re consuming.

The clinic’s patients are living in a hotspot where severe psychotic episodes have become tragically commonplace. Isiah, still waiting for his one-to-one sessions, attends group meetings meanwhile. Despite consuming less than before, he cannot stop without proper support.

“It’s there every day,” his mother Nicci says of the habit haunting their family both financially and emotionally.

A Warning Britain Cannot Ignore

As the young people at Denmark Hill create their cravings boxes, filling them with items to distract from the pull of the drug, they represent both a warning and a hope. A warning about what today’s super-strength cannabis is doing to a generation’s mental health. And hope that, with proper support, recovery remains possible.

The evidence is clear: ultra-potent cannabis poses substantial and growing dangers to young people’s mental wellbeing. The link between modern high-THC strains and serious psychiatric conditions can no longer be dismissed. As more research emerges and more families face devastating consequences, the question becomes urgent: will Britain recognise this crisis before it’s too late?

For Isiah, Katie, Aaron, Kenneth and countless others, the answer to that question could mean the difference between recovery and tragedy.

Source: The Guardian