Study register · detailFall-Kontroll-Studie (PET-Neuroimaging) · Psychosis Risk · 2014
Dopaminergic function in cannabis users and its relationship to cannabis-induced psychotic symptoms.
Bloomfield et al.·Biological Psychiatry
MixedGRADEVery low219 citations
Samplen = 38 Pat.
ControlHealthy non-users
EndpointDopamine synthesis capacity
Blindingn.a.
DesignFall-Kontroll-Studie (PET-Neuroimaging)
”Key finding
Chronic cannabis use reduces striatal dopamine synthesis capacity, without this being directly associated with cannabis-induced psychotic symptoms.
Summary
PET neuroimaging study (n=19 regular cannabis users vs. n=19 non-users); cannabis use associated with reduced striatal dopamine synthesis capacity (effect size=0,85, p=0,016); inverse correlation between cannabis use frequency and dopamine synthesis (r=-0,77, p<0,001); earlier onset of use associated with greater reduction (r=0,51, p=0,027).
P
PopulationRegular cannabis users with cannabis-induced psychotic symptoms, n=19, vs. 19 age- and sex-matched non-users
I
InterventionChronic cannabis use (naturalistic, no experimental administration)
C
ControlHealthy non-users (matched control group, n=19)
O
OutcomeReduced striatal dopamine synthesis capacity in cannabis users vs. controls (effect size 0,85; t36=2,54, p=0,016); no significant association with cannabis-induced psychotic symptoms (r=0,32, p=0,19)
Confidence in the evidence
Very lowLowModerateHigh
Very low
The lowest GRADE level, the effect estimate remains uncertain.
Downgraded for
Imprecision
Quality profile
Sample size★★★★★
Blinding—
Effect sizeMixed
Citations / year★★★★★
Authors
Bloomfield MA, Morgan CJ, Egerton A, Kapur S, Curran HV, Howes OD.
<h4>Background</h4>Cannabis is the most widely used illicit drug globally, and users are at increased risk of mental illnesses including psychotic disorders such as schizophrenia. Substance dependence and schizophrenia are both associated with dopaminergic dysfunction. It has been proposed, although never directly tested, that the link between cannabis use and schizophrenia is mediated by altered dopaminergic function.<h4>Methods</h4>We compared dopamine synthesis capacity in 19 regular cannabis users who experienced psychotic-like symptoms when they consumed cannabis with 19 nonuser sex- and age-matched control subjects. Dopamine synthesis capacity (indexed as the influx rate constant [Formula: see text] ) was measured with positron emission tomography and 3,4-dihydroxy-6-[(18)F]-fluoro-l-phenylalanine ([(18)F]-DOPA).<h4>Results</h4>Cannabis users had reduced dopamine synthesis capacity in the striatum (effect size: .85; t36 = 2.54, p = .016) and its associative (effect size: .85; t36 = 2.54, p = .015) and limbic subdivisions (effect size: .74; t36 = 2.23, p = .032) compared with control subjects. The group difference in dopamine synthesis capacity in cannabis users compared with control subjects was driven by those users meeting cannabis abuse or dependence criteria. Dopamine synthesis capacity was negatively associated with higher levels of cannabis use (r = -.77, p < .001) and positively associated with age of onset of cannabis use (r = .51, p = .027) but was not associated with cannabis-induced psychotic-like symptoms (r = .32, p = .19).<h4>Conclusions</h4>These findings indicate that chronic cannabis use is associated with reduced dopamine synthesis capacity and question the hypothesis that cannabis increases the risk of psychotic disorders by inducing the same dopaminergic alterations seen in schizophrenia.