Background: Cannabis is known to have a broad range of effects on behavior, including experiencing a “high” and tranquility/relaxation. However, there are several adverse behavioral sequalae that can arise from cannabis use, depending on frequency of use, potency (e.g., THC content), age of onset, and cumulative exposure. This systematic review examined evidence for cannabis-related adverse behavioral sequalae in otherwise healthy human subjects.Methods: Following PRISMA guidelines, we conducted a systematic review of cross-sectional and longitudinal studies from 1990 to 2020 that identified cannabis-related adverse behavioral outcomes in subjects without psychiatric and medical co-morbidities from PubMed and PsychInfo searches. Key search terms included “cannabis” OR “tetrahydrocannabinol” OR “cannabidiol” OR “marijuana” AND “anxiety” OR “depression” OR “psychosis” OR “schizophrenia” “OR “IQ” OR “memory” OR “attention” OR “impulsivity” OR “cognition” OR “education” OR “occupation”.Results: Our search detected a total of 2,870 studies, from which we extracted 124 relevant studies from the literature on cannabis effects in the non-clinical population. Effects of cannabis on several behavioral sequelae including cognition, motivation, impulsivity, mood, anxiety, psychosis intelligence, and psychosocial functioning were identified. The preponderance of the evidence suggests that frequency of cannabis use, THC (but not CBD) content, age of onset, and cumulative cannabis exposure can all contribute to these adverse outcomes in individuals without a pre-existing medical condition or psychiatric disorder. The strongest evidence for the negative effects of cannabis are for psychosis and psychosocial functioning.Conclusions: Although more research is needed to determine risk factors for development of adverse behavioral sequelae of cannabis use, these findings underline the importance of understanding vulnerability to the adverse effects of cannabis, which has implications for prevention and treatment of problematic cannabis use.

BackgroundSubstance use disorders (SUDs) are a common yet poorly studied comorbidity in individuals with psychotic disorders. The co-occurrence of the two complicates recovery and interferes with pharmacological and behavioral treatment response and adherence. Recently, researchers have been exploring both invasive and non-invasive neuromodulation techniques as potential treatment methods for SUDs. We review the evidence that neuromodulation may reduce substance craving and consumption in individuals with schizophrenia.MethodsA comprehensive literature search of PubMed, MEDLINE, and PsycINFO databases was conducted (N = 1,432). Of these, we identified seven studies examining the effects of repetitive transcranial magnetic stimulation (rTMS) and two studies using transcranial direct current stimulation (tDCS) on drug consumption and craving in schizophrenia or schizoaffective disorders.ResultsDespite the limited number of studies in this area, the evidence suggests that rTMS to the dorsolateral prefrontal cortex (DLPFC) may reduce cannabis and tobacco use in patients with schizophrenia and schizoaffective disorder. Findings with tDCS, however, were inconclusive.DiscussionOur systematic review suggests that rTMS applied to DLPFC is a safe and promising therapeutic technique for the management of comorbid schizophrenia and SUDs, with the majority of the evidence in tobacco use disorder. However, there was substantial heterogeneity in study methods, underscoring the need to optimize stimulation parameters (e.g., frequency, duration, and target regions). Larger clinical trials are needed to establish the efficacy of rTMS in reducing drug consumption and craving in psychotic patients, ideally in comparison to existing pharmacological and behavioral interventions.

Background: The association between cannabis use and psychiatric disorders has been extensively investigated, but the effect of cannabis use on the induction and persistence of psychiatric symptoms in healthy individuals is less clear. We determines whether cannabis contributes to the induction and persistence of psychotic, depressive, or (hypo)manic symptoms in healthy individuals. We identified populations that are most susceptible to these effects, in addition to cannabis use behaviors that increase the risk of developing cannabis-related psychiatric symptoms. Method: A systematic review was performed using the PubMed, Medline, and PsychInfo databases. We conducted our search using the following terms: (“cannabis” OR “tetrahydrocannabinol” OR “cannabidiol” OR “marijuana” OR “cannabinoid” OR “nabilone” OR “dronabinol” OR “nabiximols”) AND (“psycho∗” OR “mood disorder” OR “depress∗” OR “mania” OR “manic” OR “hypomania”). Experimental and observational studies published from January, 1987 to March, 2021 were considered in our analysis. Results: We assessed evidence from 47 studies, including 6 experimental studies, 28 cohort studies, and 13 cross-sectional studies. Adverse effects of cannabis or cannabinoids were found in 30/32 (93.8%) of studies reporting psychotic symptoms, 13/18 studies (72.2%) reporting depressive symptoms, and 4/4 studies (100%) reporting (hypo)manic symptoms. Cannabis use robustly increased the risk of developing psychotic and (hypo)manic symptoms, but the effects of cannabis use on depression were mixed. Risk of developing symptoms was influenced by the age of onset, tetrahydrocannabinol potency, and frequency of cannabis use. Conclusions: Cannabis use increases the risk of developing and maintaining psychotic and (hypo)manic symptoms, with mixed effects for depressive symptoms, in healthy individuals. These effects occur in a dose-dependent manner and are dependent upon THC potency. More research is necessary to understand the effects of cannabis, particularly on the induction and persistence of depressive and (hypo)manic symptoms. Contexte: L’association entre la consommation de cannabis et les troubles psychiatriques a été largement étudiée, mais l’effet de la consommation de cannabis sur l’induction et la persistance des symptômes psychiatriques chez les individus en bonne santé est moins clair. Nous avons déterminé si le cannabis contribue à l’induction et à la persistance de symptômes psychotiques, dépressifs ou (hypo)maniaques chez des individus en bonne santé. Nous avons identifié les populations les plus sensibles à ces effets, en plus des comportements de consommation de cannabis qui augmentent le risque de développer des symptômes psychiatriques liés au cannabis. Méthode: Un examen systématique a été réalisé à l’aide des bases de données PubMed, Medline et PsychInfo. Nous avons effectué notre recherche en utilisant les termes suivants: (“cannabis” OU “tétrahydrocannabinol” OU “cannabidiol” OU “marijuana” OU “cannabinoïde” OU “nabilone” OU “dronabinol” OU “nabiximols”) ET (“psycho∗” OU “trouble de l’humeur » OU « déprimé∗ » OU « manie » OU « maniaque » OU « hypomanie »).” Les études expérimentales et observationnelles publiées de janvier 1987 à mars 2021 ont été prises en compte dans notre analyse. Résultats: Nous avons évalué les résultats de 47 études, dont 6 études expérimentales, 28 études de cohorte et 13 études transversales. Des effets indésirables du cannabis ou des cannabinoïdes ont été trouvés dans 30/32 (93,8%) des études rapportant des symptômes psychotiques, 13/18 études (72,2%) rapportant des symptômes dépressifs et 4/4 études (100%) rapportant des symptômes (hypo)maniaques. La consommation de cannabis augmentait fortement le risque de développer des symptômes psychotiques et (hypo)maniaques, mais les effets de la consommation de cannabis sur la dépression étaient mitigés. Le risque de développer des symptômes était influencé par l’âge d’apparition, la puissance du tétrahydrocannabinol (THC) et la fréquence de consommation de cannabis. Conclusions: La consommation de cannabis augmente le risque de développer et de maintenir des symptômes psychotiques et (hypo)maniaques, avec des effets mitigés pour les symptômes dépressifs, chez les individus en bonne santé. Ces effets se produisent de manière proportionnelle à la dose et dépendent de la puissance du THC. Des recherches supplémentaires sont nécessaires pour comprendre ces effets du cannabis, en particulier sur l’induction et la persistance des symptômes dépressifs et (hypo)maniaques.

Amongst individuals with a mental health disorder, a comorbid diagnosis of cannabis use disorder (CUD) is associated with numerous adverse consequences, including more severe symptom profiles, poorer treatment response, and reduced psychosocial functioning. Contingency management (CM), a method to specifically reinforce target behavior attainment (e.g., substance use abstinence), may provide an effective intervention in treating cannabis use in patients with a dual diagnosis of CUD and a mental health disorder. A systematic search examining the effects of CM on cannabis use, clinical, cognitive, and psychosocial outcomes in patients with a mental health disorder on PubMed, PsycINFO, and EMBASE databases up to November 2022 was performed. Six studies met inclusion criteria for our review. We found CM to be efficacious in producing cannabis use reductions and abstinence amongst individuals with a psychotic-spectrum or major depressive disorder. Additional longitudinal studies with larger sample sizes, other psychiatric populations, and longer follow-up periods are needed to evaluate the sustained effects of CM.

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