BackgroundCannabis users present an important group for investigating putative mechanisms underlying psychosis, as cannabis-use is associated with an increased risk of psychosis. Recent work suggests that alterations in belief-updating under uncertainty underlie psychosis. We therefore compared belief updating under uncertainty between cannabis and non-cannabis users.Methods49 regular cannabis users and 52 controls completed the Space Game, via an online platform used for behavioral testing. In the task, participants were asked to predict the location of the stimulus based on previous information, under different uncertainty conditions. Mixed effects models were used to identify significant predictors of mean score, confidence, performance error and learning rate.ResultsBoth groups showed decreased confidence in high noise conditions, and increased belief updating in more volatile conditions, suggesting that they could infer the degree and sources of uncertainty. There were no significant effects of group on any of the performance indices. However, within the cannabis group, frequent users showed worse performance than less frequent users.ConclusionBelief updating under uncertainty is not affected by cannabis use status but could be impaired in those who use cannabis more frequently. This finding could show a similarity between frequent cannabis use and psychosis risk, as predictors for abnormal belief-updating.

Abstract Background Cannabis use is prevalent among individuals with psychosis and a significant risk factor for the development of psychotic disorders, leading to unfavorable outcomes. Speech changes are frequently examined in psychotic disorders and connected to clinical outcomes. However, limited research investigated the impact of cannabis use on speech, which could potentially be a crucial confounding factor in the observed speech changes associated with psychosis. This study explores the differences in speech between frequent cannabis users and matched non-users. Methods Eight-minute speech samples from frequent cannabis users (N=82) and non-users (N=82) matched for gender, age, and education were manually transcribed and analyzed. Differences in vocal, semantic, and speech connectivity features were examined using T-tests. Logistic regression and random forest classifiers were employed to evaluate the discriminatory power of speech features. Results Acoustic, semantic and connectivity measures of speech showed significant differences between groups. Frequent cannabis users exhibited more voice breaks and back vowels. Connectivity analysis revealed more one-word loops in the cannabis group. Frequent users used more words, spoke coherently, and stayed on topic. Using logistic regression and random forest classifiers, participants were classified into cannabis or non-user groups with 0.66 / 0.72 accuracy (AUC = 0.62 / 0.69) based on demographic information and speech features. Conclusions Cannabis use is associated with alterations in speech features that overlap with those observed in psychosis. Consequently, understanding and potentially accounting for the effects of cannabis use on speech would be crucial for facilitating the treatment of psychotic disorders through speech analysis.

Abstract Background and Aims Long‐term harms of cannabis may be exacerbated in adolescence, but little is known about the acute effects of cannabis in adolescents. We aimed to (i) compare the acute effects of cannabis in adolescent and adult cannabis users and (ii) determine if cannabidiol (CBD) acutely modulates the effects of delta‐9‐tetrahydocannabinol (THC). Design Randomised, double‐blind, placebo‐controlled, crossover experiment. The experiment was registered on ClinicalTrials.gov (NCT04851392). Setting Laboratory in London, United Kingdom. Participants Twenty‐four adolescents (12 women, 16‐ to 17‐year‐olds) and 24 adults (12 women, 26‐ to 29‐year‐olds) who used cannabis 0.5–3 days/week and were matched on cannabis use frequency (mean = 1.5 days/week). Intervention We administered three weight‐adjusted vaporised cannabis flower preparations: ‘THC’ (8 mg THC for 75 kg person); ‘THC + CBD’ (8 mg THC and 24 mg CBD for 75 kg person); and ‘PLA’ (matched placebo). Measurements Primary outcomes were (i) subjective ‘feel drug effect’; (ii) verbal episodic memory (delayed prose recall); and (iii) psychotomimetic effect (Psychotomimetic States Inventory). Findings Compared with ‘PLA’, ‘THC’ and ‘THC + CBD’ significantly (P < 0.001) increased ‘feel drug effect’ (mean difference [MD] = 6.3, 95% CI = 5.3–7.2; MD = 6.8, 95% CI = 6.0–7.7), impaired verbal episodic memory (MD = –2.7, 95% CI = −4.1 to −1.4; MD = −2.9, 95% CI = −4.1 to −1.7) and increased psychotomimetic effects (MD = 7.8, 95% CI = 2.8–12.7; MD = 10.8, 95% CI = 6.2–15.4). There was no evidence that adolescents differed from adults in their responses to cannabis (interaction P ≥ 0.4). Bayesian analyses supported equivalent effects of cannabis in adolescents and adults (Bayes factor [BF01] >3). There was no evidence that CBD significantly modulated the acute effects of THC. Conclusions Adolescent cannabis users are neither more resilient nor more vulnerable than adult cannabis users to the acute psychotomimetic, verbal memory‐impairing or subjective effects of cannabis. Furthermore, in adolescents and adults, vaporised cannabidiol does not mitigate the acute harms caused by delta‐9‐tetrahydocannabinol.