Abstract
SummaryBackgroundApproximately 188 million people use cannabis yearly worldwide, and it has recently been legalised in 11 US states, Canada, and Uruguay for recreational use. The potential for increased cannabis use highlights the need to better understand its risks, including the acute induction of psychotic and other psychiatric symptoms. We aimed to investigate the effect of the cannabis constituent Δ9-tetrahydrocannabinol (THC) alone and in combination with cannabidiol (CBD) compared with placebo on psychiatric symptoms in healthy people.MethodsIn this systematic review and meta-analysis, we searched MEDLINE, Embase, and PsycINFO for studies published in English between database inception and May 21, 2019, with a within-person, crossover design. Inclusion criteria were studies reporting symptoms using psychiatric scales (the Brief Psychiatric Rating Scale [BPRS] and the Positive and Negative Syndrome Scale [PANSS]) following the acute administration of intravenous, oral, or nasal THC, CBD, and placebo in healthy participants, and presenting data that allowed calculation of standardised mean change (SMC) scores for positive (including delusions and hallucinations), negative (such as blunted affect and amotivation), and general (including depression and anxiety) symptoms. We did a random-effects meta-analysis to assess the main outcomes of the effect sizes for total, positive, and negative PANSS and BPRS scores measured in healthy participants following THC administration versus placebo. Because the number of studies to do a meta-analysis on CBD's moderating effects was insufficient, this outcome was only systematically reviewed. This study is registered with PROSPERO, CRD42019136674.Findings15 eligible studies involving the acute administration of THC and four studies on CBD plus THC administration were identified. Compared with placebo, THC significantly increased total symptom severity with a large effect size (assessed in nine studies, with ten independent samples, involving 196 participants: SMC 1·10 [95% CI 0·92–1·28], p<0·0001); positive symptom severity (assessed in 14 studies, with 15 independent samples, involving 324 participants: SMC 0·91 [95% CI 0·68–1·14], p<0·0001); and negative symptom severity with a large effect size (assessed in 12 studies, with 13 independent samples, involving 267 participants: SMC 0·78 [95% CI 0·59–0·97], p<0·0001). In the systematic review, of the four studies evaluating CBD's effects on THC-induced symptoms, only one identified a significant reduction in symptoms.InterpretationA single THC administration induces psychotic, negative, and other psychiatric symptoms with large effect sizes. There is no consistent evidence that CBD induces symptoms or moderates the effects of THC. These findings highlight the potential risks associated with the use of cannabis and other cannabinoids that contain THC for recreational or therapeutic purposes.FundingUK Medical Research Council, Maudsley Charity, Brain and Behavior Research Foundation, Wellcome Trust, and the UK National Institute for Health Research.
Highlights
Cannabis is one of the most widely used psychoactive substances worldwide, with 6–7% of the population in Europe and 15·3% of the population in the USA using it each year.[1]
Evidence before this study Studies in healthy people indicate that the cannabis constituent Δ9-tetrahydrocannabinol (THC) can induce positive and negative symptoms but findings have been inconsistent
Search strategy and selection criteria For this systematic review and meta-analysis, inclusion criteria were double-blind studies that included healthy participants; reported symptom changes in response to acute administration of intravenous, oral, or inhaled THC or CBD; contained either a placebo condition or concurrent admini stration of THC plus CBD or placebo CBD; used a withinperson, crossover design; reported total, positive, or negative symptoms using BPRS or PANSS; and presented data allowing the calculation of the standardised mean difference and deviation between the THC and placebo condition
Summary
Cannabis is one of the most widely used psychoactive substances worldwide, with 6–7% of the population in Europe and 15·3% of the population in the USA using it each year.[1]. J J Moreau[4] first described an association between cannabis use and psychotic symptoms, such as paranoia and hallucinations, more than 150 years ago. Sub sequently, the main psychoactive constituent of cannabis, Δ9-tetrahydrocannabinol (THC), was shown to induce a significant increase in psychotic ( referred to as positive) symptoms as well as negative symptoms, such as poor rapport, and general psychiatric symptoms, such as depression, relative to placebo.[5] Multiple independent www.thelancet.com/psychiatry Vol 7 April 2020
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