1. Cannabis and Mental Health
4/14/2017
Cannabis and Mental Health
Sir Robin M Murray, FRS
Institute of Psychiatry,
London UK 1

2. Most people who use cannabis don’t develop problems

3. No of times cannabis taken
Swedish Army Study of Andréasson et al 1987
Cannabis Use
Psychosis
Cases of Sz
per 1,000 1 2 10
<50
>50 30 20
No of times cannabis taken
Longitudinal Studies
Risk of schizophrenia-like psychosis at age 26 years
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
15 yrs
4 yrs
18 mths
14 yrs OR
3.1
2.8
12.0
3.2
1.8
1.7
1.5
2.2
Arseneault et al 2002
Odds ratio

4. 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
THC
CBD

5. 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
THC
CBD

6. Cannabis potency in England
Skunk
THC content (%) 2 4 6 8 10 12 14
1995
1996
1997
1998
1999
2000
2001
2002
2004
Imported
Herbal
Resin
2008
Potter et al 2008, DoH, 2008

7. OR 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?
As we have seen, the study of GxE is in its very early stages.
I outlined steps we have adopted to conduct this research.
Important to step back and ask, why is it useful to do GxE studies?
What are the promises of this research?
First, Implications for neuroscience.
Psychosis
Vulnerability

9. The major unresolved issue concerns cognition
Lots of studies show that heavy cannabis users have impaired cognition
Some studies show that prolonged abstinence improves most of what has been lost
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