A team of researchers in the UK has begun a large-scale investigation into how cannabis affects the human brain, enrolling 6,000 Londoners between the ages of 18 and 45.
The Cannabis & Me project, run by King's College London, is targeting residents of the English capital who currently use cannabis, have used it fewer than three times, or have never used it at all.
Participants will begin with a 40-minute online questionnaire covering their history with cannabis and their reasons for using it — including trauma, illness, or social settings.
The survey will also examine how mood, anxiety, and shifts in thinking and perception relate to cannabis consumption patterns among those taking part.
A selected subset of participants will then be invited to attend an in-person assessment, which will include more detailed questioning, a blood test measuring CBD, THC and endocannabinoid levels, and a virtual reality scenario depicting a social situation involving cannabis.
The research team described understanding the science behind the drug as "paramount," pointing to more than 200 million daily users globally and growing consumption figures tied to expanding legalisation.
Study lead Dr Marta Di Forti said: "Cannabis is consumed daily by many recreationally, but also for medicinal reasons.
"Our study aims to provide data and tools that can make physicians in the UK and across the world more confident, where appropriate, in prescribing cannabis safely."
A parallel study will gather the same data from patients undergoing treatment for psychosis in cases where cannabis use is considered a contributing cause.
That strand of the research aims to establish whether biological factors increase an individual's vulnerability to cannabis-induced psychosis, and whether a screening tool could identify those at heightened risk.