Background: There is a substantial and unmet clinical need for pharmacological treatment of cannabis use disorders. Cannabidiol (CBD) could offer a novel treatment but it is unclear which doses might be effective or safe.Methods: Participants meeting DSM-5 cannabis use disorder criteria were allocated to four-week treatment with oral CBD at 200mg, 400mg, 800mg or placebo during a cessation attempt using a double-blinded block randomisation sequence. All received a brief psychological intervention of motivational interviewing. An adaptive Bayesian dose-finding design was used to identify effective/ineffective doses at a priori interim and final analysis stages. The primary objective was to identify the Most Effective Dose (MED) of CBD for reducing cannabis use. The primary endpoint was lower urinary THC-COOH:creatinine concentrations and/or increased days per week abstinent from cannabis during treatment, evidenced by posterior probabilities exceeding Pr=0.9 for CBD versus placebo. All analyses were intention-to-treat.Outcomes: Participants were initially randomised to placebo, 200mg, 400mg and 800mg CBD (n=48; 1:1:1:1). At interim analysis 200mg CBD was eliminated from the trial as an ineffective dose.Randomisation continued to 400mg CBD, 800mg CBD, and placebo (n=34; 1:1:1). At final analysis, both 400mg CBD and 800mg CBD exceeded primary endpoint criteria (Pr=0.9) for both primary outcomes: urinary THC-COOH:creatinine (Pr(400mg=MED │Data)=0.9995; Pr(800mg=MED │Data)=0.9965), days per week abstinent from cannabis (Pr(400mg=MED │Data)=0.9966; Pr(800mg=MED │Data)=0.9247). Compared to placebo, 400mg CBD decreased THC-COOH:creatinine concentrations by -94.21 ng/ml (95% Interval ) and increased abstinence from cannabis by 0.48 days per week (95% Interval Estimate=0.15, 0.82). Compared to placebo, 800mg CBD decreased THC-COOH:creatinine concentrations by -72.02 ng/ml (95% Interval Estimate= -135.47, -19.52) and increased abstinence from cannabis by 0.27 days per week (95% Interval Estimate= -0.09, 0.64). CBD was well tolerated with no severe adverse events and 94% completed treatment.Interpretation: In the first randomised clinical trial of CBD for cannabis use disorder, 400mg and 800mg CBD were safe and more effective than placebo at reducing cannabis use.

BackgroundCannabis and tobacco have contrasting cognitive effects. Smoking cannabis with tobacco is prevalent in many countries and although this may well influence cognitive and mental health outcomes, the possibility has rarely been investigated in human experimental psychopharmacological research.MethodThe individual and interactive effects of cannabis and tobacco were evaluated in 24 non-dependent cannabis and tobacco smokers in a randomized, placebo-controlled, double-blind, 2 (cannabis, placebo) × 2 (tobacco, placebo) crossover design. Verbal memory (prose recall), working memory (WM) performance including maintenance, manipulation and attention (N-back), psychotomimetic, subjective and cardiovascular measures were recorded on each of four sessions.ResultsCannabis alone impaired verbal memory. A priori contrasts indicated that tobacco offset the effects of cannabis on delayed recall. However, this was not supported by linear mixed model analysis. Cannabis load-dependently impaired WM. By contrast, tobacco improved WM across all load levels. The acute psychotomimetic effects and ratings of ‘stoned’ and ‘dizzy’ induced by cannabis were not altered by tobacco. Cannabis and tobacco had independent effects on increasing heart rate and interacting effects on increasing diastolic blood pressure.ConclusionsRelative to placebo, acute cannabis impaired verbal memory and WM. Tobacco enhanced performance on WM, independently of cannabis. Moreover, we found some preliminary evidence that tobacco may offset the effects of cannabis on delayed, but not immediate, verbal recall. In contrast, the psychotomimetic and subjective effects of cannabis were unaffected by tobacco co-administration. By reducing the cognitive impairment from cannabis, tobacco co-administration may perpetuate use despite adverse health consequences.

HighlightsWe studied the extent that cigarette smoking predicts level of cannabis addiction.We tested whether cigarette smoking mediates the effect of cannabis use on dependence.We interviewed 298 cannabis and tobacco users, of which 65 were followed up.Cigarette smoking accounted for 29% of the variance in cannabis dependence.Cigarette smoking mediated the relationship between cannabis use and dependence.

Levels of THC exposure are positively associated with both cannabis dependency and tolerance to the acute psychotic-like effects of cannabis. Combining urinary and self-report assessments (use frequency; age first used) enhances the measurement of cannabis use and its association with adverse outcomes.

Background Acute cannabis administration can produce transient psychotic-like effects in healthy individuals. However, the mechanisms through which this occurs and which factors predict vulnerability remain unclear. We investigate whether cannabis inhalation leads to psychotic-like symptoms and speech illusion; and whether cannabidiol (CBD) blunts such effects (study 1) and adolescence heightens such effects (study 2). Methods Two double-blind placebo-controlled studies, assessing speech illusion in a white noise task, and psychotic-like symptoms on the Psychotomimetic States Inventory (PSI). Study 1 compared effects of Cann-CBD (cannabis containing Δ-9-tetrahydrocannabinol (THC) and negligible levels of CBD) with Cann+CBD (cannabis containing THC and CBD) in 17 adults. Study 2 compared effects of Cann-CBD in 20 adolescents and 20 adults. All participants were healthy individuals who currently used cannabis. Results In study 1, relative to placebo, both Cann-CBD and Cann+CBD increased PSI scores but not speech illusion. No differences between Cann-CBD and Cann+CBD emerged. In study 2, relative to placebo, Cann-CBD increased PSI scores and incidence of speech illusion, with the odds of experiencing speech illusion 3.1 (95% CIs 1.3–7.2) times higher after Cann-CBD. No age group differences were found for speech illusion, but adults showed heightened effects on the PSI. Conclusions Inhalation of cannabis reliably increases psychotic-like symptoms in healthy cannabis users and may increase the incidence of speech illusion. CBD did not influence psychotic-like effects of cannabis. Adolescents may be less vulnerable to acute psychotic-like effects of cannabis than adults.

Rationale Chronic cannabis use is associated with impaired cognitive function. Evidence indicates cannabidiol (CBD) might be beneficial for treating cannabis use disorder. CBD may also have pro-cognitive effects; however, its effect on cognition in people with cannabis use disorder is currently unclear. Objectives We aimed to assess whether a 4-week CBD treatment impacted cognitive function. We hypothesised that CBD treatment would improve cognition from baseline to week 4, compared to placebo. Methods Cognition was assessed as a secondary outcome in a phase 2a randomised, double-blind, parallel-group and placebo-controlled clinical trial of 4-week daily 200 mg, 400 mg and 800 mg CBD for the treatment of cannabis use disorder. Participants had moderate or severe DSM-5 cannabis use disorder and intended to quit cannabis use. Our pre-registered primary cognitive outcome was delayed prose recall. Secondary cognitive outcomes were immediate prose recall, stop signal reaction time, trail-making task performance, verbal fluency and digit span. Results Seventy participants were randomly assigned to placebo (n = 23), 400 mg CBD (n = 24) and 800 mg CBD (n = 23). A 200 mg group was eliminated from the trial because it was an inefficacious dose at interim analysis (n = 12) and was not analysed here. For the primary cognitive outcome, there was no effect of CBD compared to placebo, evidenced by a lack of dose-by-time interaction at 400 mg (0.46, 95%CIs: − 1.41, 2.54) and 800 mg (0.89, 95%CIs: − 0.99, 2.81). There was no effect of CBD compared to placebo on secondary cognitive outcomes, except backwards digit span which increased following 800 mg CBD (0.30, 95%CIs: 0.02, 0.58). Conclusions In this clinical trial for cannabis use disorder, CBD did not influence delayed verbal memory. CBD did not have broad cognitive effects but 800 mg daily treatment may improve working memory manipulation. Clinical trial registration The trial was registered with ClinicalTrials.gov (NCT02044809) and the EU Clinical Trials Register (2013–000,361-36).

Cannabidiol (CBD) has shown promise in treating psychiatric disorders, including cannabis use disorder – a major public health burden with no approved pharmacotherapies. However, the mechanisms through which CBD acts are poorly understood. One potential mechanism of CBD is increasing levels of anandamide, which has been implicated in psychiatric disorders including depression and cannabis use disorder. However, there is a lack of placebo-controlled human trials investigating this in psychiatric disorders. We therefore assessed whether CBD affects plasma anandamide levels compared to placebo, within a randomised clinical trial of CBD for the treatment of cannabis use disorder. Individuals meeting criteria for cannabis use disorder and attempting cannabis cessation were randomised to 28-day administration with placebo (n = 23), 400 mg CBD/day (n = 24) or 800 mg CBD/day (n = 23). We estimated the effects of each CBD dose compared to placebo on anandamide levels from baseline to day 28. Analyses were conducted both unadjusted and adjusted for cannabis use during the trial to account for effects of cannabis on the endocannabinoid system. We also investigated whether changes in plasma anandamide levels were associated with clinical outcomes relevant for cannabis use disorder (cannabis use, withdrawal, anxiety, depression). There was an effect of 800 mg CBD compared to placebo on anandamide levels from baseline to day 28 after adjusting for cannabis use. Pairwise comparisons indicated that anandamide levels unexpectedly reduced from baseline to day 28 in the placebo group (−0.048, 95% CI [−0.089, −0.007]), but did not change in the 800 mg CBD group (0.005, 95% CI [−0.036, 0.047]). There was no evidence for an effect of 400 mg CBD compared to placebo. Changes in anandamide levels were not associated with clinical outcomes. In conclusion, this study found preliminary evidence that 28-day treatment with CBD modulates anandamide levels in individuals with cannabis use disorder at doses of 800 mg/day but not 400 mg/day compared to placebo.

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