A specialist clinic in south London, the only one of its kind in the UK, is treating patients with psychosis linked to cannabis use. The Cannabis Clinic for Patients with Psychosis, based in Denmark Hill, offers dual-diagnosis support for adults trying to reduce their cannabis consumption. It takes only 16 patients at a time, mostly men in their 20s, and has a waiting list of 14 people.
Patients like Isiah, 29, describe how cannabis use led to severe paranoia and suicidal thoughts. He first tried marijuana at 14 and became a daily user by 17. By the time he was smoking three joints a day, he felt he could trust no one. In November 2023, he climbed onto the roof of a shopping centre in Lewisham, planning to jump. He was rescued by an employee and taken to hospital.
Katie, another patient, has been sectioned 50 times and hears voices. Both attribute their mental health crises to cannabis. The clinic's clinical lead, Dr Marta Di Forti, says 74% of those who completed the intervention stopped using cannabis, and 91% of that group returned to education or work. However, she warns that waiting months for treatment increases the risk of severe psychosis and hospitalisation by three to four times.
A 2019 study by King's College London found that 12% of new psychosis cases across Europe were linked to high-potency cannabis (10% or more THC). In London, where high-potency strains dominate, the figure was 30%. Consultant Diego Quattrone, who runs a psychiatric intensive care unit, says at least 80% of new admissions report cannabis use, and daily use of high-potency cannabis is associated with violence driven by psychotic symptoms.
The clinic, run by the South London and Maudsley NHS foundation trust, offers weekly one-to-one meetings, online support sessions, and monthly brunch groups. Patients on the waiting list are welcome at brunches and receive regular telephone calls. Despite the clinic's success, demand is rising, and resources are stretched.
