Current Pharmaceutical Design - Volume 18, Issue 32, 2012

Although cannabis use disorder is strongly related to schizophrenia and treatment of patients with double diagnosis provides serious problem, specific pharmacological, molecular and therapeutical data on this subgroup are poorly available. In this paper we present a critical review on psychopharmacological boundaries of schizophrenia with concurrent cannabis use. The relevant data available in the literature suggest that a weaker compliance, poorer therapy response and higher sensitivity for extrapyramidal side effects are key features of schizophrenia and comorbid cannabis use disorder and represent a clinical challenge. Because of paucity of available research in the field there is not enough evidence to clearly depict the exact psychopharmacological profile of cannabis related schizophrenia. Further investigations are needed to assess phenotypic characteristics of this entity and to tailor effective treatment options accordingly.

Cannabis use and the development of schizophrenic psychoses share a variety of similarities. Both start during late adolescence; go along with neuropsychological deficits, reduced activity, motivation deficits, and hallucinations suggesting impairment of similar brain structures. In cannabis heavy users diminished regional gray and white matter volume was reported. Similar alterations were observed in the large literature addressing structural abnormalities in schizophrenia. Furthermore, in cannabis using schizophrenic patients, these brain alterations were especially pronounced. Close relatives of schizophrenic patients showed greater cannabis-associated brain tissue loss than non-relatives indicating a genetically mediated particular sensitivity to brain tissue loss. Possible mechanisms for the induction of structural brain alterations are here discussed including impairments of neurogenesis, disturbance of endocannabinoids and diminished neuroplasticity. Especially direct THC effects (or via endocannabinoids) may mediate diminished glutamatergic neurotransmission usually driving neuroplasticity. Correspondingly, alterations of the kynurenic acid blocking NMDA receptors may contribute to brain structure alterations. However, different cannabis compounds may exert opposite effects on the neuroanatomical changes underlying psychosis. In particular, cannabidiol (CBD) was shown to prevent THC associated hippocampal volume loss in a small pilot study. This finding is further supported by several animal experiments supporting neuroprotective properties of CBD mainly via anti-oxidative effects, CB2 receptors or adenosine receptors. We will discuss here the mechanisms by which CBD may reduce brain volume loss, including antagonism of THC, interactions with endocannabinoids, and mechanisms that specifically underlie antipsychotic properties of CBD.

Cannabis is widely used recreationally and for symptomatic relief in a number of ailments. However, cannabis has been implicated as a risk factor for the development of psychotic illness. For forty years researchers have utilised intravenous preparations of Δ9- THC, as well as several other phytocannabinoids, in a laboratory setting. The intravenous route has the most reliable pharmacokinetics, reducing inter-individual variation in bioavailability and is well suited for the delivery of synthetic compounds containing a sole pharmacological moiety. Given the association between cannabinoids and psychotic illness, there has been a resurgence of interest in experimental studies of cannabinoids in humans, and the intravenous route has been employed. Here in a critical review, we appraise the major findings from recent intravenous cannabinoid studies in humans and trace the historical roots of this work back to the 1970's.

The survival of any organism, animal or human, relies on the ability to accurately process, sense or tell time. Emerging evidence shows that timing is a crucial element in most, if not all, cognitive functioning and motor behaviour. Advances made by timing researchers provide valuable information on the neural substrates of interval timing, which indicate the involvement of certain brain areas and networks, most of which have not only been implicated in conditions such as schizophrenia, but are also abundant with cannabinoid receptors. A distorted sense of time is one of the most common effects of cannabis reported by users. In this paper, we present a critical review of the existing research on the topic. The findings are inconclusive, mainly due to methodological variations and the paucity of research. Even though 70% of time estimation studies report over-estimation, the findings of time production and time reproduction studies remain inconclusive. More research with robust methods is required to reach conclusions about the precise effect of cannabis and its active compounds on time perception. Such studies may also lead towards a better understanding of the mechanisms involved in brain functioning.

There is growing and converging evidence that cannabis may be a major risk factor in people with psychotic disorders and prodromal psychotic symptoms. The lack of available pharmacological treatments for cannabis use indicates that psychological interventions should be a high priority, especially among people with psychotic disorders. However, there have been few randomised controlled trials (RCTs) of psychological interventions among this group. In the present study we critically overview RCTs of psychological and pharmacologic interventions among people with psychotic disorders, giving particular attention to those studies which report cannabis use outcomes. We then review data regarding treatment preferences among this group. RCTs of interventions within “real world” mental health systems among adults with severe mental disorders suggest that cannabis use is amenable to treatment in real world settings among people with psychotic disorders. RCTs of manual guided interventions among cannabis users indicate that while brief interventions are associated with reductions in cannabis use, longer interventions may be more effective. Additionally, RCTs reviewed suggest treatment with antipsychotic medication is not associated with a worsening of cannabis cravings or use and may be beneficial. The development of cannabinoid agonist medication may be an effective strategy for cannabis dependence and suitable for people with psychotic disorders. The development of cannabis use interventions for people with psychotic disorders should also consider patients' treatment preferences. Initial results indicate face-to-face interventions focussed on cannabis use may be preferred. Further research investigating the treatment preferences of people with psychotic disorders using cannabis is needed.

It is widely accepted that there is a close relationship between cannabis use, the endocannabinoid system, and psychosis. In particular, cannabis use has the potential to trigger the onset of psychosis in vulnerable individuals and to exacerbate psychotic symptomatology in schizophrenia patients, including positive, negative, and cognitive symptoms. With regard to the cognitive dysfunctions as a core feature of schizophrenia, overlapping deficits in the domains of attention, memory, and executive functioning have been observed between chronic cannabis use and the disease. In this overview, we report on human clinical and experimental studies investigating the acute and chronic effects of cannabinoids on specific neurophysiological measures, i.e., the P50 suppression, the mismatch negativity, and the P300 potential, that consistently showed characteristic abnormalities in schizophrenia. Based on the results, we discuss some explanations on the putative mechanisms involving the endocannabinoid system and its interactions with other neuromodulators that might form the neural substrates underlying cannabis-induced cognitive impairments and help understand the neurobiology underpinning the development of cognitive deficits in schizophrenia.

The rate of substance use, particularly cannabis, among patients with psychosis is high and much greater than in the general population. Persistent cannabis use by patients with an established psychotic disorder adversely affects prognosis and recovery. Little agreement has been reached on the reasons that sustain cannabis use in patients with psychosis although self-report studies have shown that patients appear to use cannabis largely for the same reasons as the general population i.e. to ‘get high’ or reduce negative states such as depression and boredom. The aim of this series is to explore 5 individual cases of patients with psychosis reporting cannabis use. Full clinical assessment for each patient as well as cannabis use history, reasons for use and implications for effective treatment are explored.

Objectives: Clinical and neurobiological findings suggest that cannabinoids and their receptors are implicated in schizophrenia. Cannabidiol (CBD), a non-psychotomimetic compound of the Cannabis sativa plant, has been reported to have central therapeutic actions, such as antipsychotic and anxiolytic effects. We have recently reported that spontaneously hypertensive rats (SHR) present a deficit in contextual fear conditioning (CFC) that is specifically ameliorated by antipsychotics and aggravated by proschizophrenia manipulations. These results led us to suggest that the CFC deficit presented by SHR could be used as a model to study emotional processing impairment in schizophrenia. The aim of this study is to evaluate the effects of CBD and rimonabant (CB1 receptor antagonist) on the contextual fear conditioning in SHR and Wistar rats (WR). Methods: Rats were submitted to CFC task after treatment with different doses of CBD (experiment 1) and rimonabant (experiment 2). Results: In experiment 1, SHR showed a decreased freezing response when compared to WR that was attenuated by 1 mg/kg CBD. Moreover, all CBD-treated WR presented a decreased freezing response when compared to control rats. In experiment 2, SHR showed a decreased freezing response when compared to WR that was attenuated by 3 mg/kg rimonabant. Discussion: Our results suggest a potential therapeutical effect of CBD and rimonabant to treat the emotional processing impairment presented in schizophrenia. In addition, our results reinforce the anxiolytic profile of CBD.

Rationale: Animal and humans studies suggest that the two main constituents of cannabis sativa, delta-9-tetrahydrocannabinol (THC) and cannabidiol (CBD) have quite different acute effects. However, to date the two compounds have largely been studied separately. Objective: To evaluate and compare the acute pharmacological effects of both THC and CBD in the same human volunteers. Methods: A randomised, double-blind, cross-over, placebo controlled trial was conducted in 16 healthy male subjects. Oral THC 10 mg or CBD 600 mg or placebo was administered in three consecutive sessions, at one-month interval. Physiological measures and symptom ratings were assessed before, and at 1, 2 and 3 hours post drug administration. The area under the curve (AUC) between baseline and 3 hours, and the maximum absolute change from baseline at 2 hours were analysed by one-way repeated measures analysis of variance, with drug condition (THC or CBD or placebo) as the factor. Results: Relative to both placebo and CBD, administration of THC was associated with anxiety, dysphoria, positive psychotic symptoms, physical and mental sedation, subjective intoxication (AUC and effect at 2 hours: p<0.01), an increase in heart rate (p<0.05). There were no differences between CBD and placebo on any symptomatic, physiological variable. Conclusions: In healthy volunteers, THC has marked acute behavioural and physiological effects, whereas CBD has proven to be safe and well tolerated.

Cannabis derivatives produce their CNS effect through activation of the endocannabinoid system, a recently discovered signalling system comprising specific receptors, their intrinsic lipid ligands and the associated enzymatic machinery (transporters, biosynthetic and degradative enzymes). This review provides the latest preclinical and clinical breakthroughs on the endocannabinoid system's role in psychotic disorders such as schizophrenia. Data reported so far clearly indicate the presence of a dysregulation in the endocannabinoid system (both in term of cannabinoid receptors and endocannabinoid ligands) in animal models of psychosis as well as in schizophrenic patients. Based on these observations, the pharmacological modulation of the endocannabinoid system has been taken into account as a new therapeutic possibility for psychotic disorders. However, preclinical studies have not provided straightforward results, with both agonists and antagonists exhibiting positive, negative or even no effect. At human level, only cannabidiol, a non psychotropic phytocannabinoid, and the antagonist/inverse agonist rimonabant were tested, however additional controlled trials are required to confirm the therapeutic exploitation of these compounds. Another important aspect in studying the relationship between the endocannabinoid system and schizophrenia is the impact of Cannabis consumption on psychotic disorders, especially when this occurs at vulnerable ages such as adolescence. In fact literature from animal models support adolescence as a highly vulnerable age for the consequences of cannabis exposure on different domains (such as cognition and social behaviour) that are altered in psychotic disorders.

Cannabis is among the most widely used illicit substances. Epidemiological and neuroscientific evidence, though poorly integrated, have established a strong association between cannabis use and increased risk of psychosis. Chronic cannabis use, especially of new synthetic varieties, may trigger psychosis and precipitate schizophrenia in vulnerable individuals. However, the specific pathways by which cannabis affects brain function are unclear. It seems likely that a complex genetic-environmental interaction may underlie the link between cannabis exposure and psychosis onset, with multiple genetic variations and several environmental factors (i.e., trauma or maltreatment during childhood) involved. Also, the possible role of basic symptoms in cannabis users is still not fully acknowledged. Basic symptoms may possibly be a marker for the development of full schizophrenia in cannabis users and their recognition may play a role in prevention strategies. Moreover, the differential impact of different types of cannabis has been generally overlooked and little is known about possible pharmacological treatment approaches (with antipsychotics, cannabis agonists, cannabis antagonists) for cannabis users at risk of psychosis. The aim of the present review is to open this issue with a broad introduction on the clinical and pathophysiological link between cannabis abuse and psychosis onset.

Cannabis is the most prevalent illicit substance used among schizophrenia patients. The effects of cannabis are mediated through the endocannabinoid system, which is a major regulator of neurotransmission and may be disturbed in schizophrenia. Though cognitive impairment in schizophrenia is well established, the effects of cannabis on cognition in schizophrenia patients are still unclear. This paper reviews 19 studies that examine the cognitive effects of cannabis on schizophrenia by comparing cognitive functioning of cannabis-using and non-using schizophrenia patients across a vast range of domains (memory, attention and processing speed, executive functions, visuospatial, psychomotor and language). Of the studies included in the review, 11 reported better cognitive functions among cannabis-using schizophrenia patients compared to non-users, 5 found minimal or no difference between the groups and 3 found poorer cognitive functions among cannabis-using schizophrenia patients compared to non-users. The inconsistencies in the studies reviewed may stem from significant methodological variance between the studies regarding patient selection, adequate controls, cognitive measures used, measures of cannabis use, additional drugs used, and clinical aspects of schizophrenia. These methodological issues are discussed, as well as possible explanations for the results presented and suggestions for future research in this field.

Cannabis use is associated with a spectrum of effects including euphoria, relaxation, anxiety, perceptual alterations, paranoia, and impairments in attention and memory. Cannabis is made up of approximately 80 different cannabinoid compounds, which have synergistic or antagonistic effects on the principle active ingredient in cannabis, delta-9-tetrahydrocannabinol (THC). The net overall effect of cannabis is thought to be related to the ratio of its composite constituents; in particular, the ratio of THC to cannabidiol (CBD). Since cannabinoids induce subjective and cognitive changes that share qualitative similarities with schizophrenia, cannabinoids have been used to model psychosis. Some limitations of cannabinoid models of psychosis include the relatively high variability in experiences between different individuals, the potential for inducing unwanted effects, such as toxic psychosis in study subjects, and the lack of data showing that effective anti-psychotic treatments can reverse the behavioural and cognitive/motor effects of cannabinoids. Nabiximols (Sativex®) is an oromucosal spray containing THC and CBD in an approximate 1:1 ratio. While not extensively studied, most studies confirm that nabiximols, despite the different route of administration and presence of CBD, have similar or slightly reduced subjective/cognitive effects compared to similar doses of oral THC. While the presence of CBD may have utility in some models, it is likely that the concentrations are not high enough to meaningfully affect those aspects important for psychosis research. This review suggests that while it may present an alternative to the use of oral THC, oromucosal nabiximols may not present substantial advantages for use in psychosis research.

Cannabis use is associated with an increased risk for psychotic disorder, yet most cannabis users do not develop psychosis, suggesting that other factors are also involved. This paper reviews the available evidence suggesting that differential sensitivity to the psychosis-inducing effects of cannabis may be related to underlying genetic liability. There is robust evidence that persons at psychometric risk for psychosis are most vulnerable to display psychotic symptoms subsequent to the use of cannabis. Multiple studies have also found that persons at familial risk for psychosis have an increased sensitivity to the effects of cannabis. Together, these findings support the concept of a biological interaction between cannabis use and one's underlying genetic vulnerability. At the molecular-genetic level, however, few (if any) interactions have been consistently replicated, although a reported interaction with variation in AKT1 is promising and deserves further follow-up. The apparent lack of consistent replication can be ascribed to problems of initial gene selection, statistical power, a bias towards positive results and insufficient attempts at true replication, leading to the conclusion that increased sample sizes, greater density of genetic markers and a stronger focus on true replication are necessary. The major challenge for molecular-genetic geneenvironment interaction research will be to combine the agnostic detection of disorder-associated genetic variants from genome-wide studies with the hypothesis-based approach from epidemiological and neurobiological studies. Possible strategies for future cannabis interaction studies are discussed.

Cannabis use may be considered as an additional risk factor in a diathesis-stress model of schizophrenia where the risk of developing the illness would be higher in genetic vulnerable people. In this regard, much of the research on cannabis and psychosis is currently focusing on gene-environment interactions. The present review will focus on the interaction between genes and cannabis exposure in the development of psychotic symptoms and schizophrenia and the biological mechanisms of cannabis. Cannabis use has been shown to act together with other environmental factors such as childhood trauma or urbanicity producing synergistic dopamine sensitization effects. Studies on gene-environment interaction have mainly included genetic variants involved in the regulation of the dopaminergic system. The most promising genetic variants in this field are COMT, CNR1, BDNF, AKT1 and NRG1. Additionally, the interaction with other environmental factors and possible gene-gene interactions are considered in the etiological model.

Background: The relation between cannabis use and psychotic disorders has been investigated extensively. A series of metaanalytic reviews reveal a robust association between cannabis use and the development of psychosis and schizophrenia. However, the actual impact of cannabis use in subjects at high clinical risk for psychosis (CHR) is still unclear. Method: We conducted a systematic review of publications measuring the impact of cannabis use on CHR symptomatology and transition to a first psychotic episode. Results: Of 729 potentially relevant papers, 11 met inclusion criteria. The results of these studies were mixed. In some studies, cannabis use was associated with more severe symptoms at baseline, increased pre-psychotic symptoms immediately after intoxication, and earlier onset of certain high-risk symptoms. In others, no significant association between cannabis use and baseline symptomatology was found. In one study, cannabis use was even significantly associated with a decrease in pre-psychotic negative symptoms, and with fewer symptoms of depression and anxiety. Four out of 5 studies reported no significant effect of cannabis use on transition to psychosis. Conclusions: Cannabis use seems to provoke and enhance subclinical symptoms in CHR subjects. However, the results provide no consistent evidence for an association between cannabis use and transition to a first psychosis in CHR subjects.

Pharmacological challenge in conjunction with neuroimaging techniques has been employed for over two decades now to understand the neural basis of the cognitive, emotional and symptomatic effects of the main ingredients of cannabis, the most widely used illicit drug in the world. This selective critical review focuses on the human neuroimaging studies investigating the effects of delta-9- tetrahydrocannabinol (THC) and cannabidiol (CBD), the two main cannabinoids of interest present in the extract of the cannabis plant. These studies suggest that consistent with the polymorphic and heterogeneous nature of the effects of cannabis, THC and CBD have distinct and often opposing effects on widely distributed neural networks that include medial temporal and prefrontal cortex and striatum, brain regions that are rich in cannabinoid receptors and implicated in the pathophysiology of psychosis. They help elucidate the neurocognitive mechanisms underlying the acute induction of psychotic symptoms by cannabis and provide mechanistic understanding underlying the potential role of CBD as an anxiolytic and antipsychotic. Although there are ethical and methodological caveats, pharmacological neuroimaging studies such as those reviewed here may not only help model different aspects of the psychopathology of mental disorders such as schizophrenia and offer insights into their underlying mechanisms, but may suggest potentially new therapeutic targets for drug discovery.

A recent meta-analysis showed that the mean age of onset of psychosis among cannabis users was almost three years earlier than that of non-cannabis users. However, because cannabis users usually smoke tobacco, the use of tobacco might independently contribute to the earlier onset of psychosis. We aimed to use meta-analysis to compare the extent to which cannabis and tobacco use are each associated with an earlier age at onset of schizophrenia and other psychoses. We also examined other factors that might have contributed to the finding of an earlier age of onset among cannabis users, including the proportion of males in the samples, the diagnostic inclusion criteria and aspects of study quality. The electronic databases MEDLINE, EMBASE, PsycINFO and ISI Web of Science, were searched for English-language peer-reviewed publications that reported age at onset of schizophrenia and other psychoses separately for cannabis users and non-users, or for tobaccosmokers and non-smokers. Meta-analysis showed that the age at onset of psychosis for cannabis users was 32 months earlier than for cannabis non-users (SMD=- 0.399, 95%CI -0.493 – -0.306, z=-8.34, p<0.001), and was two weeks later in tobacco smokers compared with non-smokers (SMD=0.002, 95%CI -0.094 - 0.097, z=0.03, p=0.974). The main results were not affected by subgroup analyses examining studies of a single sex, the methods for making psychiatric diagnoses and measures of study quality. The results suggest that the association between cannabis use and earlier onset of psychosis is robust and is not the result either of tobacco smoking by cannabis using patients or the other potentially confounding factors we examined. This supports the hypothesis that, in some patients, cannabis use plays a causal role in the development of schizophrenia and raises the possibility of treating schizophrenia with new pharmacological treatments that have an affinity for endo-cannabinoid receptors.

It is unclear yet whether cannabis use is a moderating or causal factor contributing to grey matter alterations in schizophrenia and the development of psychotic symptoms. We therefore systematically reviewed structural brain imaging and post mortem studies addressing the effects of cannabis use on brain structure in psychosis. Studies with schizophrenia (SCZ) and first episode psychosis (FEP) patients as well as individuals at genetic (GHR) or clinical high risk for psychosis (ARMS) were included. We identified 15 structural magnetic resonance imaging (MRI) (12 cross sectional / 3 longitudinal) and 4 post mortem studies. The total number of subjects encompassed 601 schizophrenia or first episode psychosis patients, 255 individuals at clinical or genetic high risk for psychosis and 397 healthy controls. We found evidence for consistent brain structural abnormalities in cannabinoid 1 (CB1) receptor enhanced brain areas as the cingulate and prefrontal cortices and the cerebellum. As these effects have not consistently been reported in studies examining nonpsychotic and healthy samples, psychosis patients and subjects at risk for psychosis might be particularly vulnerable to brain volume loss due to cannabis exposure.

We conducted a systematic review on resting state cerebral blood flow activities found in first-episode psychosis (FEP) and during acute effects of cannabinoids and opioids, mental states that can be profoundly different from normal functioning. The main goal was to identify connections of cerebral blood flow measure and regional brain activity patterns associated with subjective experiences and to find out whether there are similarities between the three mental states. The present study reviewed systematically the current state of research with respect to cannabinoids and opioids on resting state activity patterns as investigated by different neuroimaging techniques. Twenty-two studies encompassing different neuroimaging techniques were selected. Cerebral perfusion and resting blood flow measure by single-photon emission computed tomography (SPECT), positron emission tomography (PET), perfusion-weighted imaging (PWI), arterial spin labeling (ASL), and resting-state functional magnetic resonance imaging (resting-state fMRI) during acute cannabinoids or opioids challenges were compared to findings in patients with FEP. The total number of subjects included in this review encompassed 279 FEP/controls (mean age = 28 ± 8.6 years, 40.1% females), 315 participants with cannabinoids (mean age = 29 ± 7.1 years, 31.8% females) and 113 participants with opioids (mean age = 30 ± 3.9 years, 17.3% females). We found that effects on regional activity were highly conflicting within the same condition group. However, we critical compared baseline acitivty patterns between FEP and acute cannabinoid or opioids effects. There was some consistent evidence suggesting positive symptoms of FEP and depersonalization experiences after cannabis administration both result in an increased anterior cingulate activity, an important area in the default mode network.

Background:Duration of untreated psychosis (DUP) is an important predictor of outcome in first-episode psychosis (FEP). Cannabis use is highly prevalent in FEP patients and it is important to evaluate the potential impact of cannabis use on DUP. Methods: A systematic review of the literature was conducted to identify articles reporting DUP in FEP cannabis users (CU+) and nonusers (CU-) respectively. Studies meeting inclusion criteria were entered into a meta-analysis. In addition, a comparative review was conducted of the relationship between substance use and DUP. Results: Nine studies were identified reporting DUP in CU+ versus CU- patients. Of the pooled sample of 1726 FEP patients, 39% were cannabis users. Although in most studies DUP was shorter in cannabis using patients, meta-analysis did not detect a significant relationship between DUP and cannabis use. A trend towards shorter DUP in substance users was also apparent in the comparative review; although in none of the studies did this association reach statistical significance. Discussion: This review and meta-analysis suggests a trend association between shorter DUP and cannabis use in FEP; especially when cannabis use is defined in terms of current or recent use (rather than lifetime use.) Further research should aim to clarify the relative effects of longstanding versus recent onset cannabis use on neurobiology, pathway to care and outcome in FEP.

Over the past years a growing research effort has investigated the relation between cannabis use and schizophrenia at a neurobiological, epidemiological and clinical level. A number of systematic reviews and meta analyses have summarized the available evidence in the field. Conversely the patient's perception of the link between cannabis use and psychosis has been under investigation. Since patient's beliefs and attitudes strongly correlate with adherence to all forms of treatment, we conducted a systematic PUBMED database search for any English and German-language articles published until January 2012 that addressed patient's perception of a cannabis psychosis link. Six studies including psychotic subjects met inclusion criteria yielding a total sample of 97. The vast majority of patients with either schizophrenia or a recent psychosis disagreed with a causal link between cannabis use and their mental illness. We qualitatively reviewed the explanatory models underlying their views, which were multi-factorial, psychological, social, biological, esoteric and irrational factors. Most patient's believed that the temporal sequence of events did not clearly indicate a causal relationship for them. They thus discarded the hypothesis of a causal link between cannabis use and psychosis. Despite the heterogeneity of the included studies, findings are comparable and support the robustness of this review. Limitations and implications for clinicians and psychosis research are discussed.

The link between cannabis and psychosis has often been debated with polarized views on the topic. There is substantial epidemiological evidence showing that cannabis increases the risk of psychosis, whereas other research suggests that schizophrenia patients self-medicate with the substance. These conflicting accounts may at least be partially explained by the two phytocannabinoids cannabidiol (CBD) and Δ 9-tetrahydrocannabinol (THC) and their opposing actions on schizophrenia-related symptoms. In the present review we will first focus on how traditional rodent models of schizophrenia have been used to improve our understanding of the propsychotic actions of THC and the antipsychotic actions of CBD. We will also review novel rodent models used to address genetic vulnerability to cannabis-induced schizophrenia and show that specific genes are being uncovered that modulate cannabinoid action (e.g. the schizophrenia susceptibility gene neuregulin 1). We will also review rodent studies that have addressed interactions between THC and CBD. These animal studies underscore great complexity with some studies showing that CBD antagonises the neurobehavioural effects of THC, while others show the opposite, that CBD potentiates the actions of THC. Various mechanisms are put forth to explain these divergent effects such as CBD antagonism at central CB1 receptors or that CBD inhibits proteins that regulate THC disposition and metabolism (e.g. the ABC transporter, P-glycoprotein).

Δ 9-tetrahydrocannabinol (Δ 9-THC) is the main compound of the Cannabis Sativa responsible for most of the effects of the plant. Another major constituent is cannabidiol (CBD), formerly regarded to be devoid of pharmacological activity. However, laboratory rodents and human studies have shown that this cannabinoid is able to prevent psychotic-like symptoms induced by high doses of Δ 9- THC. Subsequent studies have demonstrated that CBD has antipsychotic effects as observed using animal models and in healthy volunteers. Thus, this article provides a critical review of the research evaluating antipsychotic potential of this cannabinoid. CBD appears to have pharmacological profile similar to that of atypical antipsychotic drugs as seem using behavioral and neurochemical techniques in animal models. Additionally, CBD prevented human experimental psychosis and was effective in open case reports and clinical trials in patients with schizophrenia with a remarkable safety profile. Moreover, fMRI results strongly suggest that the antipsychotic effects of CBD in relation to the psychotomimetic effects of Δ 9-THC involve the striatum and temporal cortex that have been traditionally associated with psychosis. Although the mechanisms of the antipsychotic properties are still not fully understood, we propose a hypothesis that could have a heuristic value to inspire new studies. These results support the idea that CBD may be a future therapeutic option in psychosis, in general and in schizophrenia, in particular.

Several lines of experimental and clinical evidence point to a close relationship between cannabis, the endogenous cannabinoid system, and schizophrenia. A variety of animal and human studies found a dysregulation of endocannabinoid signalling in psychosis. Elevated anandamide levels in schizophrenia patients that are negatively correlated with psychotic symptomatology indicate a protective role, whereas 2-arachidonoylglycerol appears to counteract psychosis-related cognitive impairments. Thus, pharmacological manipulation of the endogenous cannabinoid system might be associated with potential antipsychotic properties. In the present systematic review, both preclinical studies using different animal models of psychosis as well as clinical trials investigating the antipsychotic effects of both cannabidiol and rimonabant are presented together with the possible underlying mechanisms of action. The results predominantly confirm the hypothesis of an antipsychotic activity of both cannabinoids. In comparison, cannabidiol appears to be superior to rimonabant with a pharmacological profile similar to atypical antipsychotic drugs.

Background: Although neurological soft signs (NSSs) have been consistently associated with schizophrenia and a variety of risk factors, few studies have focused on the association between NSSs and environmental factors such as cannabis use, particularly in patients with first episode psychosis (FEP). Aims: To review studies that have specifically investigated the association between NSSs and cannabis use in subjects who suffer from psychosis, and more specifically in FEP. Methods: A review of studies investigating the associations between neurological function in psychotic patients and cannabis use. Results: A total of 5 studies met our inclusion criteria. Two of these included data only from patients with FEP. Four studies concluded that patients with psychosis and particularly FEP who consumed cannabis showed fewer NSSs. Conclusions: Four possible explanations are suggested for the paradoxical relationship between cannabis use and NSSs in FEP. First, heavy cannabis users present with different acute responses to cannabis use than do occasional cannabis users. Second, the psychoses developed by patients who consume cannabis follow different physio-pathological pathways that include fewer neurodevelopmental abnormalities. Third, the direct effect of cannabis on the Central Nervous System (CNS) may be responsible for the paradox. Finally,severe NSSsare associated with other clinical characteristics that would limit a subject's personal access to cannabis.

Objectives: This paper aimed to critically review the current literature concerning the possible association between cannabis use and suicidal behavior in patients with psychosis and in non-psychotic samples. Methods: We performed a detailed Pubmed/Medline, Scopus, PsycLit, and PsycInfo search to identify all papers and book chapters focusing on the association between cannabis use, and suicidal behavior during the period between 1980 and 2011. Results: Most, but not all studies reported an association between suicidal behavior and cannabis use both in psychotic and non-psychotic samples. However, there were also some studies suggesting a weak (not direct) association between these two phenomena. Overall, those who attempt or complete suicide are characterized by additional risk factors such as mood disorders, stressful life events, interpersonal problems, poor social support, lonely lives, and feelings of hopelessness. Limitations: It was not possible to perform a meta-analysis due to the high heterogeneity of individual data. Conclusions: Cannabis use was a relevant risk factor associated with both suicidal attempts and behaviors in psychotic and non-psychotic samples. Preventive programs should be directed on reducing cannabis use, particularly in psychotic subjects. Evidence suggests that targeted suicide prevention programs can be also developed in specific at-risk subgroups such as those at genetic or clinical high risk of psychosis.

There is epidemiological evidence that frequent cannabis use in general and during puberty in particular increases the risk to suffer psychosis and psychotic symptoms. Based on these observations, there is growing interest in the role of the endogenous cannabinoid system (eCB system) - the point of action for psychoactive cannabinoids - in psychiatric disorders and schizophrenia in particular. It has been hypothesized nearly two decades ago that the eCB system may play a pathophysiological role in schizophrenia either in terms of an endogenous malfunction of the system itself and/or of a secondary malfunction as a result of the use of exogenous cannabinoids like Δ 9-tetrahydrocannabinol, the major psychoactive phytocannabinoid in Cannabis sativa. To test this hypothesis, several studies have been performed investigating endogenous ligands to cannabinoid CB1-receptors such as anandamide both in cerebrospinal fluid and plasma of patients and controls. Here a mini-review of the role of anandamide in schizophrenia is provided.