Cannabidiol: a Novel Intervention for Cannabis Use Problems?

Inclusion Criteria: * Aged between 16 and 60 years old. * Meet DSM-5 criteria for moderate cannabis use disorder (≥4 DSM-5 criteria) * Express desire to quit using cannabis within the next four weeks, * Have ≥1 previous failed quit attempt. * Smoke tobacco with cannabis, * Test positive for recent cannabis use according to urine analysis, * Vital signs within healthy limits and have capacity to give consent Exclusion Criteria: * Not willing to use effective contraception from when consent is taken to 6 weeks after treatment has stopped * Positive pregnancy test or breastfeeding * Allergies to the Investigational Medicinal Product (IMP) or placebo and its excipients * \>twice/month use of other illicit drugs * Outside normal Body Mass Index (BMI) * A physical health problem deemed clinically significant * The use of current prescribed psychotropic drugs * Current or prior self-reported diagnosis of a psychotic disorder * Non-English speakers due to verbal assessments.