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High-potency cannabis and the risk of psychosis

Marta Di Forti, Craig Morgan, Paola Dazzan, Carmine M. Pariante, Valeria Mondelli, Tiago Reis Marques, Rowena Handley, Sonija Luzi, Manuela Russo, Alessandra Paparelli, Alexander Butt, Simona A. Stilo, Ben Wiffen, John Powell, Robin Murray

The British Journal of Psychiatry November 30, 2009 DOI: 10.1192/bjp.bp.109.064220 (opens in new tab)

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Study at a glance

AI-extracted from the abstract
Characteristics Case-control study Peer reviewed
Sample size 454
Population People with first episode of psychosis and healthy controls from the local population
Topics Cannabis
Citations 577
Key findings Cases with first-episode psychosis were more likely to be daily cannabis users (OR = 6.4) and to have used for over 5 years (OR = 2.1). Among users, 78% of cases used high-potency cannabis versus 37% of controls (OR = 6.8), supporting the hypothesis that Delta 9-THC increases psychosis risk.

Abstract

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.

In the evidence

This study is part of the evidence base for a synthesis in the library. Here is how each one recorded it.

  • State of the evidence: Cannabis Supports

    First-episode psychosis cases were more likely to be daily users (OR 6.4), to have used over 5 years (OR 2.1), and among users 78% of cases versus 37% of controls used high-potency cannabis (OR 6.8).

    Synthesized

Comparable studies

Other observational and cohort studies on cannabis, most cited first.

Study Year Design Participants
Ayahuasca-Assisted Therapy for Addiction: Results from a Preliminary Observational Study in Canada Rural aboriginal population 2013 Observational study
Impaired cognitive performance in drug free users of recreational ecstasy (MDMA) Otherwise healthy young people 2000 Observational
Continued cannabis use and risk of incidence and persistence of psychotic symptoms: 10 year follow-up cohort study Individuals from the general population in Germany aged 14-24 at baseline 2011 Observational cohort n = 1,923
Cannabis-induced psychosis and subsequent schizophrenia-spectrum disorders: follow-up study of 535 incident cases Patients treated for cannabis-induced psychotic symptoms in Denmark between 1994 and... 2005 Observational cohort n = 535
Assessment of addiction severity among ritual users of ayahuasca Regular ayahuasca users (jungle-based and urban-based) and matched controls 2010 Observational cohort n = 127

Citations in the library

Cited by 94

and 89 more in the library

Cites 5

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