Cannabis contains delta-9-tetrahydrocannabinol (THC), which causes intoxication. People who use cannabis frequently often develop tolerance, meaning they need to use more THC to feel the same effects. Cannabidiol (CBD) is another compound found in cannabis that is not intoxicating and may influence how THC affects the body and brain.
This study will examine whether taking CBD changes how much THC heavy cannabis users consume to reach their usual level of intoxication. The study will also develop a new laboratory method that allows participants to safely and gradually self-administer THC using a vaporiser, similar to how cannabis is used in real-world settings.
The study will include around 30 adults who use cannabis heavily. In the first stage, participants will take part in pilot sessions to help refine the THC administration procedure. In the second stage, participants will attend two study sessions and receive a single oral dose of CBD or placebo, in a random order. After this, they will inhale THC using a vaporiser and decide when to stop based on how intoxicated they feel.
Researchers will measure how much THC is used, along with mood, mental health symptoms, thinking abilities, physical measures such as heart rate and blood pressure, and blood levels of THC and CBD. The results will help improve understanding of cannabis tolerance and whether CBD alters responses to THC in heavy cannabis users.
Adults, between 18 and 45 years old
Heavy and frequent cannabis user: using 7-14 grams of high potency cannabis per week over the past month, and using cannabis on at least 5 days per week over the past month
Positive urine drug screen (UDS) for cannabis
Willing to abstain from cannabis use for 4 hours before any experimental session.
Dependent use of alcohol or illicit drugs (apart from cannabis or tobacco/nicotine)
Not able to provide a UDS which is negative for illicit drugs (apart from cannabis)
Not able to provide a negative alcohol breath test
Personal or family history (first-degree) of psychosis or mania
King's College London
Lead sponsor
South London and Maudsley NHS Foundation Trust
Collaborator