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The effects of cannabis on memory function in users with and without a psychotic disorder: findings from a combined meta-analysis

Published online by Cambridge University Press:  10 September 2015

T. Schoeler ,
J. Kambeitz ,
I. Behlke ,
R. Murray  and
S. Bhattacharyya
T. Schoeler
Affiliation:
Department of Psychosis Studies, Institute of Psychiatry, Psychology & Neuroscience, King's College London, De Crespigny Park, London SE5 8AF, UK
J. Kambeitz
Affiliation:
Department of Psychosis Studies, Institute of Psychiatry, Psychology & Neuroscience, King's College London, De Crespigny Park, London SE5 8AF, UK Department of Psychiatry, Ludwig-Maximilian-University Munich, Nuβbaumstr. 7, 80336 Munich, Germany
I. Behlke
Affiliation:
Department of Psychosis Studies, Institute of Psychiatry, Psychology & Neuroscience, King's College London, De Crespigny Park, London SE5 8AF, UK Institute of Psychology, Univeristy of Osnabrueck, Seminarstr. 20, 49074 Osnabrueck, Germany
R. Murray
Affiliation:
Department of Psychosis Studies, Institute of Psychiatry, Psychology & Neuroscience, King's College London, De Crespigny Park, London SE5 8AF, UK
S. Bhattacharyya*
Affiliation:
Department of Psychosis Studies, Institute of Psychiatry, Psychology & Neuroscience, King's College London, De Crespigny Park, London SE5 8AF, UK
*
*Address for correspondence: S. Bhattacharyya, M.B.B.S., M.D., Ph.D., Department of Psychosis Studies, Institute of Psychiatry, King's College London, De Crespigny Park, London SE5 8AF, UK. (Email: [email protected])
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Abstract

Background.

Effect of cannabis use on memory function is a contentious issue, with effects being different in healthy individuals and patients with psychosis.

Method.

Employing a meta-analytic approach we investigated the effects of cannabis use on memory function in patients with psychosis and healthy individuals, and the effect of diagnosis, memory dimension and moderating factors. A total of 88 studies were identified through a systematic literature search, investigating healthy (n = 7697) and psychotic (n = 3261) individuals. Standardized mean differences between the cannabis user and non-user groups on memory tasks were estimated using random-effects models and the effect-size statistic Cohen's d. Effects of potential moderating factors were tested using mixed-effects models and subgroup analyses.

Results.

We found that cannabis use was associated with significantly (p ⩽ 0.05) impaired global (d = 0.27) and prospective memory (d = 0.61), verbal immediate (d = 0.40) and delayed (d = 0.36) recall as well as visual recognition (d = 0.41) in healthy individuals, but a better global memory (d = −0.11), visual immediate recall (d = −0.73) and recognition (d = −0.42) in patients. Lower depression scores and younger age appeared to attenuate the effects of cannabis on memory. Cannabis-using patients had lower levels of depression and were younger compared with non-using patients, whilst healthy cannabis-users had higher depression scores than age-matched non-users. Longer duration of abstinence from cannabis reduced the effects on memory in healthy and patient users.

Conclusions.

These results suggest that cannabis use is associated with a significant domain-specific impairment in memory in healthy individuals but not in cannabis-using patients, suggesting that they may represent a less developmentally impaired subgroup of psychotic patients.

Keywords

Cannabismemorymeta-analysespsychosisΔ-9-tetrahydrocannabinol
Type
Original Articles
Information
Psychological Medicine , Volume 46 , Issue 1 , January 2016 , pp. 177 - 188
Copyright
Copyright © Cambridge University Press 2015 

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