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Daily and high potency cannabis are linked to higher rates of psychosis, study finds

BMJ 2019; 364 doi: https://doi.org/10.1136/bmj.l1290 (Published 20 March 2019) Cite this as: BMJ 2019;364:l1290
  1. Nigel Hawkes
  1. London

Almost a third of new cases of psychosis in London are linked to the use of high potency cannabis, a study has concluded.1

The pioneering multicentre study set out to discover the incidence of psychosis in 10 sites in Europe and one in Brazil and to investigate any links with cannabis use.

High potency

Current evidence on the incidence of psychosis is “pathetic,” said Robin Murray of the Institute of Psychiatry at King’s College, London, at a briefing held at the Science Media Centre on 19 March. “So is the evidence on the potency of cannabis being used in different places.”

The research team set out to change this by recording new diagnoses of psychosis in 1130 people aged 18 to 64 in the 11 sites and by questioning the people with new diagnoses and matched control participants about their use of cannabis. The findings, published in Lancet Psychiatry,1 showed an eightfold variation in incidence …

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