Introduction
Cannabis, or marijuana, is the most used illegal substance in most countries, including United Kingdom and USA. Currently, about 20% of young people reported cannabis at least once a week or regular consumption (consumption> 100 times). Consumption has grown particularly in early adolescence, when the developing brain may be especially susceptible to environmental exposures
. Experimental studies
and consumer studies provide strong evidence that cannabis intoxication can produce psychotic and affective experiences
usually transient and mild. Of greater concern are the chronic symptoms that persist beyond or occur independently of the effects of intoxication.
It is unclear whether cannabis increases the incidence of established symptoms such as schizophrenia or depression but this issue is important because these disorders cause significant discomfort to individuals, their families and the public treasury for the cost of health care.
is unlikely that Randomized controlled trials (RCTs) of medical use of cannabis will be helpful for answering this question of causality, since there are substantial differences between the pharmacokinetic profiles of such preparations and consumed cannabis as a recreational drug. The follow-up periods typically shorter clinical trials also substantially hinder the interpretation of results.
Previous reviews in this field have not been very systematic, comprehensive examined psychosocial effects that mental illness or have included cross-sectional data. We systematically reviewed longitudinal studies of cannabis use and subsequent psychotic effects or affective mental health and assessed the strength of the evidence that cannabis use and these effects are causally related.
Methods Study selection and data collection studies were included if they were longitudinal and population-based or case-control studies nested within longitudinal designs. Cohort excluded persons with mental illness or problems related to drug use, studies of prison populations and RCTs of cannabis for medical use.
Results for psychosis diagnoses included: schizophrenia, schizophreniform, schizoaffective or psychotic and non-affective psychosis affective psychosis
otherwise specified, psychotic symptoms, delusions, hallucinations or thought disorder. The presence of delusions, hallucinations or thought disorder was a requirement for all purposes of psychosis.
affective disorder, mood or bipolar affective disorder not otherwise specified, depression, suicidal thoughts or suicide attempts, anxiety, neurosis, and mania were included in the emotional effects. We
in different databases from inception to September 5, 2006: Medline, Embase, Cumulative Index to Nursing Literature and Allied Health (CINAHL) access OVID, PsycINFO WebSPIRS access; ISI Web of Knowledge, ISI Proceedings, ZETOC (British database of journals and conference contents) EDINA BIOSIS in Health Sciences in Latin America and the Caribbean (LILACS) and Literature Health Sciences Caribbean (MEDCARIB). We
using the entry "([psychosis or schizophrenia or synonyms] or [affective disorder or depression or synonyms]) and (cannabis or synonyms)", using text words and indexing terms (MeSH) (The details are complete available on the departmental website to GL).
The search was restricted to studies in humans but was not limited by language or study design. We
literature included studies and wrote to experts in the field and researchers responsible for the studies to find other relevant studies published or not. We examined all titles and abstracts and obtained full texts of potentially relevant articles. Working independently and in duplicate, we read the articles and determine if they met the inclusion criteria
sion using a registry eligibility criteria (available on the departmental website of each author.)
resolve disagreements by consensus and extracted data independently and in duplicate. Evaluate the quality of the studies as such were collected in each potential non-causal explanations, particularly bias and confounding factors. We appreciate the information on the strategy of the sample, response rates, data loss, losses and attempts to reverse the reverse causation, intoxication effects and confounding factors.
Data synthesis
When considering the characteristics of the studies were reasonably homogeneous, group them and combine the data in a meta-analysis; of
contrary, we present a summary of the data told. Combine studies using the random effects model of DerSimonian and Laird and the command of Stata ® mess (9.0). When studies presented data for subgroups only these were incorporated as separate studies. We value diversity using estadísticaI2. We investigated the presence of publication bias using funnel plots and Egger test. A summary of compliance with MOOSE guidelines is available on GL's departmental website.
role of study sponsor
The study sponsor had no role in study design, data collection, data analysis, data interpretation or writing the report. The corresponding author had full access to all study data and was ultimately responsible for the decision to submit for publication. Results
searches of bibliographies in electronic databases, the advice of experts and searching bibliographies of included studies and other reviews provided
4804 references. According to their titles and abstracts believe that 175 (3-6%) of these references contain enough detail to potentially be relevant. We excluded 143 of these references may not be relevant once you read the full article. The details of the studies that were excluded at this stage, including those we regard as near misses, are available on the departmental web
GL.
found 11 studies of psychosis, these reports presented data from seven cohort studies. There were five adult population-based cohort: the Epidemiologic Catchment Area Study (ECA) of the USA, the study of premature infants
Development Stages of Psychopathology (EDSP) in Germany, the Netherlands Mental Health Survey and Incidence Study (NEMESIS) Study National Psychiatric Morbidity (NMPS) of UK and Swedish Cohort Records.
There were two birth cohorts, of Dunedin and Christchurch (CHDS) in New Zealand. To los registros suecos y las cohortes CHDS, se incluyeron los datos de los informes más recientes en cada caso ya que tenían periodos de seguimientos más largos para cubrir más eventos y tenían análisis más completos para reducir al mínimo la causalidad reversa y los efectos de confusión. La omisión de individuos con esquizofrenia simple no dio resultados diferentes para la esquizofrenia en el estudio de registros sueco (Zammit S, no publicado). Sin embargo, no se incluyeron los resultados de la psicosis no esquizofrénica de esta cohorte, debido a que los códigos diagnósticos que se usaron incluían potencialmente a muchas personas sin psicosis según como se define en este estudio.
Tres selected studies examined psychotic disorders were defined as the presence of psychotic symptoms with concomitant evidence of limited performance (Dunedin, NEMESIS, and Swedish records) and six studies used the broader effects of psychotic symptoms, without the requirement limited operation (CHDS, Dunedin, ECA, EDSP, NEMESIS and NMPS.
For affective outcomes, there were 24 reports of 15 cohort studies: two birth cohorts from New Zealand (CHDS and Dunedin), six cohorts based U.S. adult population (Berkeley, ECA, and state of NY,) and UK (NMPS [J Haynes, University of Bristol, personal communication]), Australia (Mental Health Service Northern Rivers, NoRMHS), and Colombia, and seven school population-based cohort of Australia (Victoria) and USA (AddHealth, Baltimore,
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