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Cannabis and Mental Health Sir Robin M Murray, FRS Institute of Psychiatry, London UK

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Presentation on theme: "Cannabis and Mental Health Sir Robin M Murray, FRS Institute of Psychiatry, London UK"— Presentation transcript:

1 Cannabis and Mental Health Sir Robin M Murray, FRS Institute of Psychiatry, London UK robin.murray@kcl.ac.uk

2 Most people who use cannabis don’t develop problems

3 Swedish Army Study of Andréasson et al 1987 0 1 2 10 <50 >50 30 20 10 0 No of times cannabis taken Cases of Sz per 1,000 Arseneault et al 2002 Risk of schizophrenia-like psychosis at age 26 years Odds ratio Country Sweden NL NZ (Chr) NZ (Dun) Germany UK Australia n 50,053 4,045 18,000 1,265 1,253 2,436 8,500 3,800 FU 25 yrs 3 yrs Retro 3 yrs 15 yrs 4 yrs 18 mths 14 yrs OR 3.1 2.8 12.0 3.2 1.8 3.1 1.7 1.5 2.2 Longitudinal Studies Psychosis

4 THC The ingredients of cannabis Tetrahydrocannabinol (THC) – partial agonist at CB1 High doses cause impairment of attention, memory and learning, hallucinations and paranoid ideas Cannabidiol (CBD) – inverse agonist at CB1 Is not hallucinogenic Has anxiety relieving properties Antagonises effects of THC CBD

5 THC The ingredients of cannabis THC causes Impairment of attention, memory and learning Hallucinations and paranoid ideas Cannabidiol (CBD) Is not hallucinogenic Has anxiety relieving properties Antagonises effects of THC CBD

6 Cannabis potency in England Potter et al 2008, DoH, 2008 THC content (%) 0 2 4 6 8 10 12 14 199519961997199819992000200120022004 2008 Skunk Imported Herbal Resin

7 Risk of being a Psychotic Case (OR adjusted for gender, age, ethnicity, Stimulants, level of Ed) OR

8 Why do only some cannabis users go psychotic? Psychosis Vulnerability Cannabis Use

9 The major unresolved issue concerns cognition 1)Lots of studies show that heavy cannabis users have impaired cognition 2)Some studies show that prolonged abstinence improves most of what has been lost 3)Last year follow-up of the Dunedin cohort reported that those who had started using cannabis as adolescent had lost 8 points of IQ by 38 years


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