• Tom P Freeman, Celia J A Morgan, Chandni Hindocha, Gráinne Schafer, Ravi K Das, and H Valerie Curran.
• Clinical Psychopharmacology Unit, University College London, London, UK.
• Addiction. 2014 Oct 1; 109 (10): 1686-94.

Aims(1) To determine whether measured concentrations of delta-9-tetrahydrocannabinol (THC) and cannabidiol (CBD) in individuals' own cannabis predict their estimates of drug potency and actual titration; and (2) to ascertain if these effects are influenced by frequency of use and cannabis type.DesignCross-sectional, naturalistic.SettingParticipants' own homes.ParticipantsA total of 247 cannabis users in the United Kingdom: 152 'recreational' (1-24 days/month) and 95 'daily' (≥25 days/month).MethodsParticipants rated their own cannabis for its potency (1-10) and type ('resin', 'herbal', 'skunk') before smoking it in front of the researcher. The amount of cannabis (g) used in their joints was recorded and an additional sample was analysed for THC and CBD concentrations (%).FindingsTHC concentrations were related negatively to the amount of cannabis used [unstandardized regression coefficient: b = -0.009, 95% confidence interval (CI) = -0.017, -0.002]. Potency estimates were predicted by increasing THC (b = 0.055, 95% CI = 0.020, 0.090) and decreasing CBD (b = -0.160, 95% CI = -0.284, -0.062), and both of these associations were mediated by cannabis type (THC: b = 0.018, 95% CI = 0.006, 0.037; CBD: b = -0.105, 95% CI = -0.198, -0.028). Potency estimates were more reflective of THC as frequency of use increased (b = 0.004, 95% CI = 0.001, 0.007) and were 7.3 times more so in daily (partial r = 0.381) than recreational users (r = 0.052).ConclusionsWhen using their own cannabis in a naturalistic setting, people titrate the amount they roll in joints according to concentrations of delta-9-tetrahydrocannabinol (THC) but not cannabidiol (CBD). Recreational users thus show poor understanding of cannabis potency.© 2014 Society for the Study of Addiction.

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