Cannabis-induced attenuated psychotic symptoms: implications for prognosis in young people at ultra-high risk for psychosis.
BACKGROUND
Cannabis use shows a robust dose-dependent relationship with psychosis risk among the general population. Despite this, it has been difficult to link cannabis use with risk for transitioning to a psychotic disorder among individuals at ultra-high risk (UHR) for psychosis. The present study examined UHR transition risk as a function of cannabis use characteristics which vary substantially between individuals including age of first use, cannabis abuse severity and a history of cannabis-induced attenuated psychotic symptoms (APS).


METHODS
Participants were 190 UHR individuals (76 males) recruited at entry to treatment between 2000 and 2006. They completed a comprehensive baseline assessment including a survey of cannabis use characteristics during the period of heaviest use. Outcome was transition to a psychotic disorder, with mean time to follow-up of 5.0 years (range 2.4-8.7 years).


RESULTS
A history of cannabis abuse was reported in 58% of the sample. Of these, 26% reported a history of cannabis-induced APS. These individuals were 4.90 (95% confidence interval 1.93-12.44) times more likely to transition to a psychotic disorder (p = 0.001). Greater severity of cannabis abuse also predicted transition to psychosis (p = 0.036). However, this effect was mediated by higher abuse severity among individuals with a history of cannabis-induced APS.


CONCLUSIONS
Findings suggest that cannabis use poses risk in a subpopulation of UHR individuals who manifest cannabis-induced APS. Whether this reflects underlying genetic vulnerability requires further study. Nevertheless, findings reveal an important early marker of risk with potentially significant prognostic utility for UHR individuals.
Orygen,The National Centre for Excellence in Youth Mental Health,35 Poplar Road,Parkville,VIC 3052,Australia.
M J
MJ
McHugh
Orygen,The National Centre for Excellence in Youth Mental Health,35 Poplar Road,Parkville,VIC 3052,Australia.
P D
PD
McGorry
Institute of Brain, Behaviour and Mental Health,University of Manchester,Manchester,UK.
A R
AR
Yung
Telethon Kids Institute,University of Western Australia,WA 6008,Australia.
A
A
Lin
Orygen,The National Centre for Excellence in Youth Mental Health,35 Poplar Road,Parkville,VIC 3052,Australia.
S J
SJ
Wood
Orygen,The National Centre for Excellence in Youth Mental Health,35 Poplar Road,Parkville,VIC 3052,Australia.
J A
JA
Hartmann
Orygen,The National Centre for Excellence in Youth Mental Health,35 Poplar Road,Parkville,VIC 3052,Australia.
B
B
Nelson
D000293:Adolescent; D000328:Adult; D002188:Cannabis / Q000009:adverse effects*; D018450:Disease Progression; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D008297:Male; D002189:Marijuana Abuse / Q000150:complications*; D011379:Prognosis; D011605:Psychoses, Substance-Induced / Q000209:etiology*; D012306:Risk; D055815:Young Adult
Cannabis; psychosis; ultra-high risk