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Background and aims Addictive behaviours are among the greatest scourges on humankind. It is important to estimate the extent of the problem globally and in different geographical regions. Such estimates are available, but there is a need to collate and evaluate these to arrive at the best available synthetic figures. Addiction has commissioned this paper as the first of a series attempting to do this. Methods Online sources of global, regional and national information on prevalence and major harms relating to alcohol use, tobacco use, unsanctioned psychoactive drug use and gambling were identified through expert review and assessed. The primary data sources located were the websites of the World Health Organization (WHO), the United Nations Office on Drugs and Crime (UNODC) and the Alberta Gambling Research Institute. Summary statistics were compared with recent publications on the global epidemiology of addictive behaviours. Results An estimated 4.9% of the world's adult population (240 million people) suffer from alcohol use disorder (7.8% of men and 1.5% of women), with alcohol causing an estimated 257 disability-adjusted life years lost per 100 000 population. An estimated 22.5% of adults in the world (1 billion people) smoke tobacco products (32.0% of men and 7.0% of women). It is estimated that 11% of deaths in males and 6% of deaths in females each year are due to tobacco. Of ‘unsanctioned psychoactive drugs’, cannabis is the most prevalent at 3.5% globally, with each of the others at

Objectives: This study aims to (1) elucidate whether the Hawthorne effect exists, (2) explore under what conditions, and (3) estimate the size of any such effect. Study Design and Setting: This systematic review summarizes and evaluates the strength of available evidence on the Hawthorne effect. An inclusive definition of any form of research artifact on behavior using this label, and without cointerventions, was adopted. Results: Nineteen purposively designed studies were included, providing quantitative data on the size of the effect in eight randomized controlled trials, five quasiexperimental studies, and six observational evaluations of reporting on one’s behavior by answering questions or being directly observed and being aware of being studied. Although all but one study was undertaken within health sciences, study methods, contexts, and findings were highly heterogeneous. Most studies reported some evidence of an effect, although significant biases are judged likely because of the complexity of the evaluation object. Conclusion: Consequences of research participation for behaviors being investigated do exist, although little can be securely known about the conditions under which they operate, their mechanisms of effects, or their magnitudes. New concepts are needed to guide empirical studies. 2014 The Authors. Published by Elsevier Inc.

SUMMARY An engineering-economic analysis of the behaviours of each of two pre-combustion gas-turbine combined cycles with CO2 capture (an Integrated Gasification Combined Cycle (IGCC) and an Integrated Reforming Combined Cycle (IRCC)) is described. Their economic performances have been evaluated in terms of the break-even electricity selling price. The results show that the proposed pre-combustion power plant efficiency values (37% and 43.7% for the IGCC and the IRCC respectively) are significantly lower compared to a conventional plant value (55.3%). The CO2 emissions of the latter are less than half those of the conventional plant. Introducing an hypothetical carbon tax equal to 50£/tCO2, the break-even selling price (BESP) for the proposed IGCC and IRCC plants is 4.40 p/kWh and 4.10 p/kWh respectively, while for the conventional plant amounts to 4.73 p/kWh. A sensitivity analysis has been carried out by varying the most influential investment parameters. The analysis has revealed that, considering the uncertainties associated with these key parameters, a substantial risk that the BESP could exceed the first value obtained is so prominent in some cases to alter their ranking order with respect to the most competitive technology. The final part of the analysis is a Monte-Carlo simulation to determine the impact of simultaneous variations of all the variables, subject to uncertainty, on the break-even selling unit price for the generated electricity. From the simulation, it derives that the BESP value ranges from 3.13 p/kWh to over 6.00 p/kWh for the IGCC case with a 50% probability of exceeding the first value obtained (4.40 p/kWh). In the IRCC case, the range of possible value for the BESP is from 2.85 p/kWh to 6.10 p/kWh, and there is a 60% probability that the actual BESP would exceed the first value obtained (4.10 p/kWh). Copyright © 2013 John Wiley & Sons, Ltd.

Reducing CO2-emissions from electricity-generating power-plants is a high priority. Several advanced low-carbon power-plants have gained wide acceptance. Uncertainties concerning future costs and performances of new pertinent technologies and unit fuel-prices as well as the types and the comprehensiveness of CO2-emissions regulations exacerbate the difficulty of selecting promising candidates to be considered for future investments. A computer-based Monte-Carlo simulation technique has been devised to help choose the best technology for financial investments: it allows for the stated uncertainties and assesses the trade-offs between expected returns and the key risks imposed on decision makers. The economic-modelling methodology is described. The computer-based model assesses the investment in a new low-carbon integrated reforming combined-cycle (IRCC) power-plant. The worthwhileness of this financial investment is evaluated in terms of net present-value (NPV), internal rate-of-return (IRR) and pay-back period (PBP).

Turbulent flame speeds were measured over a range of pressures to 0·8 MPa using a jet flow apparatus fired with a synthetic mixture representing a mid-European natural gas. The equivalence ratio O was 0·9. The gas contained significant proportions of ballast gases and higher hydrocarbons. The method adopted was the ‘flame angle’ technique, using schlieren imaging to obtain the flame vertex angle from the peak density gradient. Image analysis techniques were developed to reduce interpretation errors and give an unbiased result. The data show higher flame speeds than those obtained with pure methane at elevated pressures, using similar methodology, and has an application in numerical modelling of combustors.

The study investigates patient preferences and beliefs and treatment program factors related to the decision to prescribe either buprenorphine or methadone to opiate-dependent patients. The sample (N = 192) was recruited from 10 addiction treatment services in London. Data were collected by means of a single structured interview conducted with patients commencing a treatment episode at the participating agencies. Data on patient demographics, beliefs, attitudes, and preferences were collected using a structured interview. Data regarding treatment goals and prescribed medication were collected from interviews with clinical staff. Oral methadone had a higher preference rating than buprenorphine. Clinical prescribing practices were influenced by patient preferences (both positive and negative), by prior treatment experiences, and by current treatment goals. Patient preferences and beliefs about opioid agonist medications served as an important influence upon clinical prescribing practices. The odds of being prescribed buprenorphine were three times greater among those patients who reported a preference for buprenorphine. The odds of receiving a prescription for methadone were about twice as great among those for whom methadone was the more preferred medication. Preferences were related to previous treatment experiences with these opioid agonists, and for patients in both groups, personal experience was the most important source of information about the treatment options. Buprenorphine was more likely to be prescribed for short-term detoxification and methadone for maintenance treatment.

The concept of sensible drinking is not new and can be traced back to at least the 4th century BC. In the mid-to-late 1980s, United Kingdom policy converged on a safe limit of 21 units of alcohol per week for men and 14 units per week for women. These were adopted into ‘The Health of the Nation’ that established targets for the reduction of those drinking more than these limits. In 1995, the Department of Health published a report entitled ‘Sensible drinking’ that promoted a daily limit of 3–4 units for men and 2–3 units for women. Weekly and daily recommendations running in parallel have resulted in a confusing public health message. A decade later the ‘Health of the Nation’ targets have not been achieved: While the proportion of males drinking more than the weekly limits has remained the same around 28%, the percentage of women doing so has actually increased from 11% to 17%. Clearly the sensible drinking message is not working but currently there is nothing better to replace it.

The study uses a school-based sample to test the social and familial risk and protective factors relating to cannabis use. Based on a self-completion survey of 2078 14-16-year-olds (mean age of 15 years) attending seven standard state-run secondary schools in south London, an assessment was made of rates and risk factors for cannabis use. Twenty-four per cent of the total sample had ever used cannabis, with 15% having done so in the month prior to assessment. In addition to greater likelihood of illicit drug use, lifetime cannabis users were less likely to spend time regularly with both their mothers and fathers, but more likely to spend free time with friends who smoked, drank alcohol and used illicit drugs, and with friends involved in criminal activities. Among those who had ever used cannabis, frequency of cannabis use was predicted (using linear regression) by two onset factors (earlier initiation of drinking and cannabis use were both linked to more frequent use) and two social factors (more time spent with drug-using friends and less time spent with the mother). Overall, the study showed that early onset, itself predicted by social networks, is linked to more frequent use of cannabis and that this appears to be sustained by less time spent with parents and more with drug-using peers.

Changes in criminal convictions were investigated among 1075 clients admitted to 54 drug misuse treatment services across England as part of the National Treatment Outcome Research Study (NTORS). Convictions data during the year prior to treatment, and at 1 year, 2 years, and 5 years after treatment intake were collected from the Home Office Offenders' Index, a national database of all convictions in adult and youth courts. Clinical data were collected by face-to-face interviews at intake to treatment, and at follow-up 1 year, 2 years, and 4-5 years after admission to treatment. During the year prior to treatment, 34% of the sample had been convicted of at least one offence. Conviction rates at all follow-up points were significantly lower than at intake. During the year prior to the 5-year follow-up, 18% of the sample had been convicted of at least one offence. Statistically significant reductions in the mean number of convicted offences were also found between treatment intake and 5-year follow-up. Reductions in convictions were found for acquisitive, drug selling, and violent crimes. Reductions in crime were associated with reductions in regular heroin use, age, and with stable housing. The results replicate previously reported findings of crime reductions among the NTORS cohort as indicated by self-reported measures of offending behaviour. The observed reductions in crime among drug misusers after treatment represent substantial changes in behaviour and have considerable personal, social and clinical significance. Reduced criminality also provides substantial economic benefits to society.

The increase in cocaine use in young people has been reflected in an increase in the number of deaths in which cocaine is identified post mortem. This increase is evident in relation to police custody deaths. In the current analysis, 43 drug-related deaths in custody are considered with cocaine identified in 24 of the post mortem examinations. The article examines the characteristics of these deaths, with particular attention paid to the method and related reasons for drug consumption. Crucially, these deaths contrast with national drug mortality data as they generally involve cocaine consumed by swallowing at the point of arrest. A total of 18 of 24 cocaine deaths involved oral ingestion with at least 15 of these possible attempts at drug concealment occurring at the point of arrest. There is likely to be a considerable risk of loss of life among street-level drug dealers who swallow to avoid drug detection; the article examines the risks associated with this behaviour and possible preventative strategies.

The article uses a semi-structured interview method to assess the acquisition, preparation and use of heroin in a cohort of 114 drug users in contact with treatment services in south-east London, and examines the impact of the increase in crack availability on heroin use and preparation in this population. Seventy-six participants reported using heroin on a daily basis, involving an average of 2.8 hits and using a mean of 0.75 g on each using day. Although almost all of the sample bought their own heroin, very few were confident of assessing its quality, and the mean estimated purity level of heroin bought was 22.7%. Similarly, most of the sample believed that the heroin purchased was adulterated and, although most believed that the heroin quality was evident during the preparation stage, relatively few would ask about quality at the point of purchase, and it is apparent that the beliefs held by much of the sample about drug purity issues did not impact upon their behaviour. Seventy individuals reported t...

The study assessed prevalence of volatile substance abuse (VSA), and its link to other forms of psychoactive substance use and to other problem behaviours among 14–15 year olds recruited from sixteen secondary schools in south-west London. Lifetime use of volatile substances was reported by 126 young people (6% of the sample) whose mean age of first use was 12.6 years. Using logistic regression analysis, lifetime use of volatile substances was found to be associated with more frequent cigarette smoking and more frequent drinking in the previous month, with higher levels of anxiety, greater involvement in delinquent acts, and lower levels of educational aspirations. Among volatile substance abusers, more frequent use was associated with higher levels of psychological distress and greater delinquent activity. Volatile substance abuse may be a marker for other forms of substance use and for other behaviour problems. This issue remains inadequately explored by researchers and clinicians.

While dual diagnosis research has often focussed on substance misuse disorders among mental health clients, relatively little is known about comparable rates of dual diagnosis in community mental health and substance misuse settings because of, inter alia, limitations and lack of consistency in screening. In the current study clinicians administered a brief screening tool, which detects problematic alcohol, drug use, psychosis and common mental health symptoms, to 50 substance misuse and 50 mental health treatment attenders. Sixty-four per cent of the total sample screened positive for dual diagnosis (positive for any psychiatric disorder and either a drug or alcohol problem). Highest rates were observed in the alcohol sample (92.3%), followed by the drug sample (87.5%), and lowest in the community mental health (CMHT) sample (38%). Current depression and social phobia were most prevalent in alcohol clients compared to psychosis, mania and suicidal ideation in CMHT clients. Around one-third of CMHT clients reported using drugs (mainly cannabis) and around a fifth reported problematic alcohol use. The study demonstrates the feasibility of incorporating a dual diagnosis screen into routine clinical practice. The screen can be used in both mental health and substance misuse treatment settings, which are evidently managing complex client caseloads.

Addictive behaviours are among the greatest scourges on humankind. It is important to estimate the extent of the problem globally and in different geographical regions. Such estimates are available, but there is a need to collate and evaluate these to arrive at the best available synthetic figures. Addiction has commissioned this paper as the first of a series attempting to do this.Online sources of global, regional and national information on prevalence and major harms relating to alcohol use, tobacco use, unsanctioned psychoactive drug use and gambling were identified through expert review and assessed. The primary data sources located were the websites of the World Health Organization (WHO), the United Nations Office on Drugs and Crime (UNODC) and the Alberta Gambling Research Institute. Summary statistics were compared with recent publications on the global epidemiology of addictive behaviours.An estimated 4.9% of the world's adult population (240 million people) suffer from alcohol use disorder (7.8% of men and 1.5% of women), with alcohol causing an estimated 257 disability-adjusted life years lost per 100 000 population. An estimated 22.5% of adults in the world (1 billion people) smoke tobacco products (32.0% of men and 7.0% of women). It is estimated that 11% of deaths in males and 6% of deaths in females each year are due to tobacco. Of 'unsanctioned psychoactive drugs', cannabis is the most prevalent at 3.5% globally, with each of the others at 1%; 0.3% of the world's adult population (15 million people) inject drugs. Use of unsanctioned psychoactive drugs accounts for an estimated 83 disability-adjusted life years lost per 100 000 population. Global estimates of problem gambling are not possible, but in countries where it has been assessed the prevalence is estimated at 1.5%.Tobacco and alcohol use are by far the most prevalent addictive behaviours and cause the large majority of the harm. However, the quality of data on prevalence and addiction-related harms is mostly low, and comparisons between countries and regions must be viewed with caution. There is an urgent need to review the quality of data on which global estimates are made and coordinate efforts to arrive at a more consistent approach.

The future's bright, the future's green. Well almost. Just when things were looking up for medical cannabis, the Government pulled the plug and refused it a license. Is this just a blip on the rocky road to legal cannabis products? Or, as many fear, does it signal the end of medical cannabis and possible liquidation for GW Pharmaceuticals, the developer? John Witton, the UK's leading voice on cannabis, speaks to the key players and asks just what got up the nose of the regulators and what, if anything, GW can do to recover.

Opioids are very addictive drugs because of their powerful effects on reward and pain pathways in the brain. Opioid addiction is currently a worldwide problem and injecting heroin presents serious health risks including death from overdose. The increase in the nonmedical use of prescription opioids and the increase in overdose deaths are worrying trends in North America. There is therefore an increasing need for access to effective treatments. The 2 major drug treatments, methadone and buprenorphine, have proven efficacy but are not necessarily administered in the most effective doses or under optimum conditions. Alternative approaches such as slow-release oral morphine, tincture of opium, and the use of the opioid antagonist naltrexone to maintain abstinence are used seemingly effectively in some countries but have yet to be fully evaluated in randomized controlled trials. Heroin-assisted treatment has proven to be a valuable and effective treatment when administered in specialized clinics but is only appropriate for those who have failed to improve on optimal methadone or buprenorphine maintenance. Recent innovations and substitution treatment as an alternative to incarceration are described. Drug treatment of opioid addiction is most effective when administered as part of a therapeutic program as demonstrated in the initial methadone evaluations and the more recent trials with heroin-assisted treatment.

Publisher Summary This chapter examines the extent to which treatment is primarily driven by the patient’s best interests, as opposed to the interests of government, the treatment industry, and the pharmaceutical industry. Drug use can be initially considered a matter of personal responsibility, and persistent use despite experiencing harm may be considered a failure of personal responsibility. It seems plausible to hypothesize that there is a subpopulation of heroin users that is more likely to take risks, less likely to be deterred by social disapproval or penal sanctions, and particularly vulnerable to developing the chronic, relapsing type of addiction. A divergence of views about the most effective way to use methadone is compatible with the assumption that opioid substitution treatment (OST) is at least a well-intentioned attempt to improve the health of heroin addicts. Ethical concerns over OST go further. Prescribing opioids to heroin addicts is counterintuitive and from its inception has challenged the dominant paradigm of addiction treatment, which is based on the principle that abstinence is necessary for recovery from addiction.

A decision-support framework has been developed to evaluate options for reducing carbon-dioxide emissions from the power-generation sector. The framework is based on the so-called T.E.R.A. (Techno-economic environmental risk analysis) method conceived at Cranfield University. It is based essentially on a robust power-plant performance model, coupled with a variety of additional modules (emissions, economic, technology-risk analysis). The evaluation tool performs screening over multiple options by means of modelling and assessment of several metrics that represent possible advantages and risks for a given assessment case. A case study on a CCS-based technology is reported to illustrate the application of the framework.

BackgroundThe concept of demand characteristics, which involves research participants being aware of what the researcher is investigating, is well known and widely used within psychology, particularly in laboratory-based studies. Studies of this phenomenon may make a useful contribution to broader consideration of the effects of taking part in research on participant behaviour. This systematic review seeks to summarise data from studies of the effects of demand characteristics on participant behaviours in non-laboratory settings.Methodology/Principal FindingsElectronic databases were searched to identify eligible studies. These had to be purposely designed to evaluate possible effects of demand characteristics on at least one behavioural outcome under the autonomous control of the participants and use longitudinal study designs. Only 7 studies were included, 6 providing observational data and 1 experimental study, with 5 studies involving examination of possible effects on health behaviours. Although studies provided some evidence of effects of demand characteristics on participant behaviour, heterogeneous operationalisation of the construct, the limited number of studies and poor quality of study designs made synthesis and interpretation of study findings challenging.Conclusions/SignificanceAlthough widely accepted as important in psychology, there have been few dedicated studies of the effects of demand characteristics on research participant behaviours outside laboratory settings. This body of literature does not currently contribute to the wider study of research participation effects. A systematic review of data from laboratory-based studies is needed, as are high-quality primary studies in non-laboratory settings. We suggest that unqualified use of the term demand characteristics should be abandoned.

BACKGROUND: The possible effects of research assessments on participant behaviour have attracted research interest, especially in studies with behavioural interventions and/or outcomes. Assessments may introduce bias in randomised controlled trials by altering receptivity to intervention in experimental groups and differentially impacting on the behaviour of control groups. In a Solomon 4-group design, participants are randomly allocated to one of four arms: (1) assessed experimental group; (2) unassessed experimental group (3) assessed control group; or (4) unassessed control group. This design provides a test of the internal validity of effect sizes obtained in conventional two-group trials by controlling for the effects of baseline assessment, and assessing interactions between the intervention and baseline assessment. The aim of this systematic review is to evaluate evidence from Solomon 4-group studies with behavioural outcomes that baseline research assessments themselves can introduce bias into trials. METHODOLOGY/PRINCIPAL FINDINGS: Electronic databases were searched, supplemented by citation searching. Studies were eligible if they reported appropriately analysed results in peer-reviewed journals and used Solomon 4-group designs in non-laboratory settings with behavioural outcome measures and sample sizes of 20 per group or greater. Ten studies from a range of applied areas were included. There was inconsistent evidence of main effects of assessment, sparse evidence of interactions with behavioural interventions, and a lack of convincing data in relation to the research question for this review. CONCLUSIONS/SIGNIFICANCE: There were too few high quality completed studies to infer conclusively that biases stemming from baseline research assessments do or do not exist. There is, therefore a need for new rigorous Solomon 4-group studies that are purposively designed to evaluate the potential for research assessments to cause bias in behaviour change trials.

CO 2 emissions reduction has become a major issue for the power generation sector. Advanced technology development and deployment are among the most frequently advocated keys to solving this great challenge, since the present configurations are unlikely to meet the demanding environmental requirements. This paper presents a methodical approach intended to evaluate the maturity level and the future development potential of environmental friendly power plants coupling Monte Carlo simulation technique and the concept of Technology Readiness Level (TRL). Although the numerical results are speculative, the paper offers insights into the validity of the method proposed as a means to addressing the role of technological innovation in the power generation sector to meet global climate stability targets.

Summary points About a third of adults in the UK have tried cannabis, and 2.5 million people, mostly 16-29 year olds, have used it in the past year.1 Although most people who smoke cannabis will develop neither severe mental health problems nor dependence, regular use of cannabis may be associated with a range of health, emotional, behavioural, social, and legal problems, particularly in young, pregnant, and severely mentally ill people.2 3 The past decade has seen a shift in available cannabis preparations from resinous “hash” to intensively grown high potency herbal preparations, often referred to as skunk, which now dominates the UK market.4 Compared with traditional cannabis preparations, skunk tends to have higher levels of tetrahydrocannabinol, the main psychoactive constituent of cannabis, and lower levels of the anxiolytic cannabinoid cannabidiol. In January 2009 cannabis was returned to its original class B classification (from class C) under the UK Misuse of Drugs Act. Despite high levels of use, only 6% of those seeking treatment for substance misuse in England cite cannabis as their …

BackgroundControversy remains as to whether cannabis acts as a causal risk factor for schizophrenia or other functional psychotic illnesses.AimsTo examine critically the evidence that cannabis causes psychosis using established criteria of causality.MethodWe identified five studies that included a well-defined sample drawn from population-based registers or cohorts and used prospective measures of cannabis use and adult psychosis.ResultsOn an individual level, cannabis use confers an overall twofold increase in the relative risk for later schizophrenia. At the population level, elimination of cannabis use would reduce the incidence of schizophrenia by approximately 8%, assuming a causal relationship. Cannabis use appears to be neither a sufficient nor a necessary cause for psychosis. It is a component cause, part of a complex constellation of factors leading to psychosis.ConclusionsCases of psychotic disorder could be prevented by discouraging cannabis use among vulnerable youths. Research is needed to understand the mechanisms by which cannabis causes psychosis.

This preliminary test of a brief intervention designed to stimulate GP incorporation of cannabis enquiry was followed up after 2-3 months. Intervention comprised face-to-face discussion based on principles of motivational interviewing, with informational adjunct. Substantially more positive attitudes and greater clinical activity were observed following receipt of intervention.

The policy debate on cannabis has moved back into prominence in Britain and elsewhere after reports of increases in use during the early 1990s1 and renewed claims about the therapeutic value of marijuana. 2 3 Rational debate has often been obstructed because the media present a forced choice between two sets of views. One of these constructed views is that cannabis is harmless when used recreationally, is therapeutically useful, and hence should be legalised. The other is that recreational use is harmful to health and that cannabis should continue to be prohibited for recreational or therapeutic purposes.4 This oversimplification of the cannabis debate has prevented a more considered examination of eight conceptually separate issues (box). We believe that a competent consideration of these issues would contribute to a more informed debate about the appropriate public policies that could be adopted towards cannabis use for recreational or therapeutic purposes. #### Summary points Cannabis use is increasing steadily in many countries and is most prevalent among young people The value of the debate on cannabis is seriously diminished by heated contributions that obstruct rational consideration of important public health and policy issues The different domains of the debate should be considered in isolation at first to allow a more objective analysis of the evidence Substantial public investment in research into the different areas is a prerequisite of rational consideration of public policies More than 60 different cannabinoids and over 400 active components have been identified in samples of cannabis.2 However, our interest and concerns about associated harms could be much more focused. Should we be especially concerned about the use of new cannabis preparations with higher concentrations of tetrahydrocannabinol? Does using cannabis that has a higher tetrahydrocannabinol content result in a higher intake of tetrahydrocannabinol or do smokers consciously or subconsciously titrate …

There is a wealth of informative websites for those interested in substance misuse. Those sites listed here may be useful first ports of call for readers seeking comprehensive introductions to available resources, research and current thinking about all aspects of addictions (details correct at time of going to press).

Adults suffering from psychosis have high rates of cannabis use. However, there remains controversy as to whether this is a cause or consequence of the psychosis. This review tests the hypothesis that cannabis can cause psychosis by reviewing studies verifying three important criteria for causality in psychiatry: association, temporal priority, and direction, with the emphasis put on prospective longitudinal population-based studies that tested temporal priority. Evidence supports a causal role for cannabis in the development of psychosis but it appears that cannabis use is neither a sufficient nor a necessary cause for psychosis. Rather, it is a component cause - part of a complex constellation of factors leading to psychosis. On an individual level, cannabis use appears to confer only a two-to three-fold increase in the relative risk for later schizophrenia. On a population level, elimination of cannabis use could lead to a 7-13% reduction in incidence of schizophrenia. Thus, some cases of psychotic disorder could be prevented by discouraging cannabis use, particularly among vulnerable youths. More research is needed to better understand the mechanisms by which cannabis causes psychosis.