Endurance

• Research type

  Research Study

• Full title

  Exploring the effect of cannabidiol on cannabis tolerance using a Novel vaporiser Device in heavy Users: a RANdomised placebo-Controlled Experimental study

• IRAS ID

  352814

• Contact name

  Edward Chesney

• Contact email

  edward.chesney@kcl.ac.uk

• Sponsor organisation

  King's College London and South London and Maudsley NHS Foundation Trust

• Duration of Study in the UK

  1 years, 11 months, 31 days

• Research summary

  Cannabidiol (CBD) shows potential as a treatment for psychosis and cannabis addiction. It is safe, well-tolerated, and has few side effects. Unlike tetrahydrocannabinol (THC), the psychoactive part of cannabis, CBD only causes mild effects at very high doses. Some studies suggest that CBD can reduce THC’s negative effects when taken orally or through an IV, but studies using inhaled CBD have not shown this.

  In a recent study, we gave oral CBD (1000mg) or a placebo to people with cannabis addiction and schizophrenia before they were given THC. Unexpectedly, CBD worsened the effects of THC on psychosis and thinking skills. We thought this might be due to how CBD affects THC levels in the blood, but our tests found no differences.

  A problem with past research is that it used fixed doses of THC over short periods. This doesn’t match real-life cannabis use, where people adjust their dose to feel the effects they want.

  This study has two goals:

  To create a lab model of gradual cannabis intoxication. Heavy cannabis users will use a handheld vaporizer to self-administer small THC doses until they reach their limit.
  To test how CBD affects cannabis tolerance in this lab model.

  We will recruit people who use cannabis regularly. Most participants will complete three sessions, an initial assessment, and then two experiments each lasting one day. The sessions will be completed in a clinical research lab at King's College Hospital in London. Participants will be given CBD/placebo capsules in the morning, inhale cannabis with a vape pen in the afternoon, provide blood samples, and complete assessments of their mental health, cognition, and speech. They will have time to sober up before they go home at the end of the day.

• REC name

  East Midlands - Leicester Central Research Ethics Committee

• REC reference

  25/EM/0158

• Date of REC Opinion

  24 Jul 2025

• REC opinion

  Further Information Favourable Opinion