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

20 de setembro de 20155min11

Psychological Medicine

Original Articles

T. Schoelera1, J. Kambeitza1a2, I. Behlkea1a3, R. Murraya1 and S. Bhattacharyyaa1 c1

a1 Department of Psychosis Studies, Institute of Psychiatry, Psychology & Neuroscience, King’s College London, De Crespigny Park, London SE5 8AF, UK

a2 Department of Psychiatry, Ludwig-Maximilian-University Munich, Nuβbaumstr. 7, 80336 Munich, Germany

a3 Institute of Psychology, Univeristy of Osnabrueck, Seminarstr. 20, 49074 Osnabrueck, Germany


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.

(Received September 03 2014)

(Revised July 29 2015)

(Accepted August 04 2015)

Key words

  • Cannabis;
  • memory;
  • meta-analyses;
  • psychosis;
  • Δ-9-tetrahydrocannabinol


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:

Sobre a UNIAD

A Unidade de Pesquisa em álcool e Drogas (UNIAD) foi fundada em 1994 pelo Prof. Dr. Ronaldo Laranjeira e John Dunn, recém-chegados da Inglaterra. A criação contou, na época, com o apoio do Departamento de Psiquiatria da UNIFESP. Inicialmente (1994-1996) funcionou dentro do Complexo Hospital São Paulo, com o objetivo de atender funcionários dependentes.


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