Cannabis and Mental Health

1
Cannabis and Mental Health
Sir Robin M Murray, FRS Institute of
Psychiatry, London UK robin.murray_at_kcl.ac.uk
2
Most people who use cannabis dont develop
problems
3
Swedish Army Study of Andréasson et al 1987
Cases of Sz per 1,000
Longitudinal Studies
Risk of schizophrenia-likepsychosis at age 26
years

• FU
• 25 yrs
• 3 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

• Country
• Sweden
• NL
• NL
• NL
• NZ (Chr)
• NZ (Dun)
• Germany
• UK
• Australia

• n
• 50,053
• 4,045
• 4,045
• 18,000
• 1,265
• 1,253
• 2,436
• 8,500
• 3,800

Arseneault et al 2002
Oddsratio
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

CBD
THC
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
Imported Herbal
Resin
2008
Potter et al 2008, DoH, 2008
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?
Cannabis Use
Psychosis
Vulnerability
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