Paola Dazzan

BACKGROUND: The risk of individuals having adverse effects from drug use (eg, alcohol) generally depends on the frequency of use and potency of the drug used. We aimed to investigate how frequent use of skunk-like (high-potency) cannabis in south London affected the association between cannabis and psychotic disorders. METHODS: We applied adjusted logistic regression models to data from patients aged 18-65 years presenting to South London and Maudsley NHS Foundation Trust with first-episode psychosis and population controls recruited from the same area of south London (UK) to estimate the effect of the frequency of use, and type of cannabis used on the risk of psychotic disorders. We then calculated the proportion of new cases of psychosis attributable to different types of cannabis use in south London. FINDINGS: Between May 1, 2005, and May 31, 2011, we obtained data from 410 patients with first-episode psychosis and 370 population controls. The risk of individuals having a psychotic disorder showed a roughly three-times increase in users of skunk-like cannabis compared with those who never used cannabis (adjusted odds ratio [OR] 2·92, 95% CI 1·52-3·45, p=0·001). Use of skunk-like cannabis every day conferred the highest risk of psychotic disorders compared with no use of cannabis (adjusted OR 5·4, 95% CI 2·81-11·31, p=0·002). The population attributable fraction of first-episode psychosis for skunk use for our geographical area was 24% (95% CI 17-31), possibly because of the high prevalence of use of high-potency cannabis (218 [53%] of 410 patients) in our study. INTERPRETATION: The ready availability of high potency cannabis in south London might have resulted in a greater proportion of first onset psychosis cases being attributed to cannabis use than in previous studies. FUNDING: UK National Institute of Health Research (NIHR) Specialist Biomedical Research Centre for Mental Health, SLaM and the Institute of Psychiatry at King's College London, Psychiatry Research Trust, Maudsley Charity Research Fund, and th European Community's Seventh Framework Program grant (agreement No. HEALTH-F2-2009-241909 [Project EU-GEI]).

BACKGROUND: People who use cannabis have an increased risk of psychosis, an effect attributed to the active ingredient Delta 9-tetrahydrocannabinol (Delta 9-THC). There has recently been concern over an increase in the concentration of Delta 9-THC in the cannabis available in many countries. AIMS: To investigate whether people with a first episode of psychosis were particularly likely to use high-potency cannabis. METHOD: We collected information on cannabis use from 280 cases presenting with a first episode of psychosis to the South London & Maudsley National Health Service (NHS) Foundation Trust, and from 174 healthy controls recruited from the local population. RESULTS: There was no significant difference between cases and controls in whether they had ever taken cannabis, or age at first use. However, those in the cases group were more likely to be current daily users (OR = 6.4) and to have smoked cannabis for more than 5 years (OR = 2.1). Among those who used cannabis, 78% of the cases group used high-potency cannabis (sinsemilla, 'skunk') compared with 37% of the control group (OR 6.8). CONCLUSIONS: The finding that people with a first episode of psychosis had smoked higher-potency cannabis, for longer and with greater frequency, than a healthy control group is consistent with the hypothesis that Delta 9-THC is the active ingredient increasing risk of psychosis. This has important public health implications, given the increased availability and use of high-potency cannabis.

BACKGROUND: The incidence of schizophrenia in the African-Caribbean population in England is reported to be raised. We sought to clarify whether (a) the rates of other psychotic disorders are increased, (b) whether psychosis is increased in other ethnic minority groups, and (c) whether particular age or gender groups are especially at risk. METHOD: We identified all people (n=568) aged 16-64 years presenting to secondary services with their first psychotic symptoms in three well-defined English areas (over a 2-year period in Southeast London and Nottingham and a 9-month period in Bristol). Standardized incidence rates and incidence rate ratios (IRR) for all major psychosis syndromes for all main ethnic groups were calculated. RESULTS: We found remarkably high IRRs for both schizophrenia and manic psychosis in both African-Caribbeans (schizophrenia 9.1, manic psychosis 8.0) and Black Africans (schizophrenia 5.8, manic psychosis 6.2) in men and women. IRRs in other ethnic minority groups were modestly increased as were rates for depressive psychosis and other psychoses in all minority groups. These raised rates were evident in all age groups in our study. CONCLUSIONS: Ethnic minority groups are at increased risk for all psychotic illnesses but African-Caribbeans and Black Africans appear to be at especially high risk for both schizophrenia and mania. These findings suggest that (a) either additional risk factors are operating in African-Caribbeans and Black Africans or that these factors are particularly prevalent in these groups, and that (b) such factors increase risk for schizophrenia and mania in these groups.

CONTEXT: Convention suggests uniformity of incidence of schizophrenia and other psychoses; variation would have implications for their causes and biological characteristics. OBJECTIVE: To investigate variability in the incidence of psychotic syndromes in terms of place, ethnicity, age, and sex. DESIGN: Three-center, prospective, comprehensive survey of clinically relevant first-onset psychotic syndromes over a 2-year period (1997-1999). Census data provided the denominator. SETTING: Southeast London, Nottingham, and Bristol, England. PARTICIPANTS: One million six hundred thousand person-years yielded 568 subjects aged 16 to 64 years with clinically relevant psychotic syndromes. MAIN OUTCOME MEASURES: The World Health Organization Psychosis Screen and the Schedules for Clinical Assessment in Neuropsychiatry to classify, blind to ethnicity, all DSM-IV psychotic syndromes and the subclasses of schizophrenia, other nonaffective disorders, affective disorders, and substance-induced psychosis. RESULTS: All syndromes showed a characteristic age distribution. Schizophrenia was significantly more common in men (incidence rate ratio [IRR], 2.3 [95% confidence interval (CI), 1.7-3.1]); affective disorders occurred equally in men and women (IRR, 1.0 [95% CI, 0.7-1.3]). All psychoses were more common in the black and minority ethnic group (crude IRR, 3.6 [95% CI, 3.0-4.2]). Differences in age, sex, and study center accounted for approximately a quarter of this effect (adjusted IRR, 2.9 [95% CI, 2.4-3.5]) in each psychosis outcome. The age-sex standardized incidence rate for all psychoses was higher in Southeast London (IRR, 49.4 [95% CI, 43.6-55.3]) than Nottingham (IRR, 23.9 [95% CI, 20.6-27.2]) or Bristol (IRR, 20.4 [95% CI, 15.1-25.7]). Rates of all outcomes except affective disorders remained significantly higher in Southeast London when the model was expanded to control for ethnicity. CONCLUSIONS: There is significant and independent variation of incidence of schizophrenia and other psychoses in terms of sex, age, ethnicity, and place. This confirms that environmental effects at the individual, and perhaps neighborhood level, may interact together and with genetic factors in the etiology of psychosis.