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Sub-chronic impact of cannabinoids in street cannabis on cognition, psychotic-like symptoms and psychological well-being

Published online by Cambridge University Press:  29 July 2011

C. J. A. Morgan*
Clinical Psychopharmacology Unit, UCL, Gower Street, London WC1E 6BT, UK
C. Gardener
Clinical Psychopharmacology Unit, UCL, Gower Street, London WC1E 6BT, UK
G. Schafer
Clinical Psychopharmacology Unit, UCL, Gower Street, London WC1E 6BT, UK
S. Swan
Clinical Psychopharmacology Unit, UCL, Gower Street, London WC1E 6BT, UK
C. Demarchi
Clinical Psychopharmacology Unit, UCL, Gower Street, London WC1E 6BT, UK
T. P. Freeman
Clinical Psychopharmacology Unit, UCL, Gower Street, London WC1E 6BT, UK
P. Warrington
Clinical Psychopharmacology Unit, UCL, Gower Street, London WC1E 6BT, UK
I. Rupasinghe
Clinical Psychopharmacology Unit, UCL, Gower Street, London WC1E 6BT, UK
A. Ramoutar
Clinical Psychopharmacology Unit, UCL, Gower Street, London WC1E 6BT, UK
N. Tan
Clinical Psychopharmacology Unit, UCL, Gower Street, London WC1E 6BT, UK
G. Wingham
Clinical Psychopharmacology Unit, UCL, Gower Street, London WC1E 6BT, UK
S. Lewis
Clinical Psychopharmacology Unit, UCL, Gower Street, London WC1E 6BT, UK
H. V. Curran
Clinical Psychopharmacology Unit, UCL, Gower Street, London WC1E 6BT, UK
*Address for correspondence: Dr C. J. A. Morgan, Clinical Psychopharmacology Unit, University College London, Gower St, London WC1E 6BT, UK. (Email:



Cannabis varies considerably in levels of its two major constituent cannabinoids – (delta-9-tetrahydrocannabinol (THC) and cannabidiol (CBD). Recently, we found evidence that those who smoked cannabis containing detectable levels of CBD had fewer psychotic-like symptoms than those whose cannabis had no CBD. The present study aimed, first, to replicate those findings and, second, to determine whether protective effects of CBD may extend to other harms of cannabis, such as memory impairment and reduced psychological well-being.


A total of 120 current cannabis smokers, 66 daily users and 54 recreational users were classified into groups according to whether analysis of their hair revealed the presence or absence of CBD and high versus low levels of THC. All were assessed on measures of psychosis-like symptoms, memory (prose recall; source memory) and depression/anxiety.


Lower psychosis-like symptoms were found in those whose hair had CBD compared with those without. However, this was seen only in recreational users, who had higher levels of THC in their hair. Higher THC levels in hair were associated with increased depression and anxiety. Prose recall and source memory were poorer in daily users with high THC levels in hair while recognition memory was better in individuals with CBD present in hair.


CBD attenuates the psychotic-like effects of cannabis over time in recreational users. Higher THC negatively impacts on memory and psychological well-being. These findings raise concerns for the harms stemming from use of varieties such as ‘skunk’ (sensimillia), which lack any CBD but currently dominate the supply of cannabis in many countries.

Original Articles
Copyright © Cambridge University Press 2011

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