High-potency cannabis and the risk of psychosis.
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.


OBJECTIVE
To investigate whether people with a first episode of psychosis were particularly likely to use high-potency cannabis.


METHODS
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.
Di Forti
Marta
M
Department of Psychiatry, Institute of Psychiatry, De Crespigny Park, London SE5 8AF, UK. m.diforti@iop.kcl.ac.uk
Morgan
Craig
C
Dazzan
Paola
P
Pariante
Carmine
C
Mondelli
Valeria
V
Marques
Tiago Reis
TR
Handley
Rowena
R
Luzi
Sonija
S
Russo
Manuela
M
Paparelli
Alessandra
A
Butt
Alexander
A
Stilo
Simona A
SA
Wiffen
Ben
B
Powell
John
J
Murray
Robin M
RM
D000293:Adolescent; D000328:Adult; D000367:Age Factors; D000368:Aged; D002188:Cannabis / Q000737:chemistry*; D016022:Case-Control Studies; D013759:Dronabinol / Q000009:adverse effects*; D005260:Female; D006801:Humans; D008131:London; D008297:Male; D008385:Marijuana Smoking / Q000009:adverse effects*; D008875:Middle Aged; D011605:Psychoses, Substance-Induced / Q000209:etiology*; D012307:Risk Factors; D055815:Young Adult
D013759:Dronabinol