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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

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.

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.

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.

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.

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 …

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.