Study register · detailMeta-Analyse · Psychosis · 2016
The effects of cannabis on memory function in users with and without a psychotic disorder: findings from a combined meta-analysis
Schoeler et al.·Psychological MedicineImpact 4.3
MixedGRADEHigh95 citations
Samplek = 88 Studien n = 10.958 Pat.
Durationunclear
ControlNon-cannabis users
EndpointMemory function
Blindingunklar
DesignMeta-Analyse
”Key finding
Cannabis use was associated with significant memory impairments in healthy individuals, but with improved memory in patients with psychotic disorders.
Summary
Meta-analysis across k=88 studies (n=10.958: 7.697 healthy, 3.261 psychosis patients) on cannabis effects on memory. In healthy individuals: cannabis associated with impairments in global memory (d=0.27), prospective memory (d=0.61), verbal immediate (d=0.40) and delayed recall (d=0.36), visual recognition (d=0.41). In psychosis patients paradoxically better global memory (d=-0.11), visual immediate recall (d=-0.73) and recognition (d=-0.42). Cannabis-using patients were younger and had lower depression scores.
P
PopulationAdults with and without psychosis, healthy individuals (n=7.697) and patients with psychotic disorder (n=3.261)
I
InterventionCannabis use (various patterns, not an intervention in the experimental sense)
C
ControlNon-cannabis users (healthy and psychotic control groups)
O
OutcomeHealthy individuals: significant memory impairments (global memory d=0,27; prospective memory d=0,61; verbal immediate memory d=0,40; verbal delayed memory d=0,36; visual recognition d=0,41); patients: better global memory (d=−0,11), better visual immediate memory (d=−0,73) and recognition (d=−0,42) in cannabis users vs. non-users
Confidence in the evidence
Very lowLowModerateHigh
High
The highest of four GRADE levels, the effect estimate is very reliable.
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.