Cannabis and Response Inhibition in People at Clinical High Risk for Psychosis
A small controlled study found adverse cognitive responses to smoked cannabis in participants at clinical high risk for psychosis. It raises a susceptibility question without establishing a diagnostic test or proving that all people with that risk respond alike.
A carefully selected, very small sample
Madden and colleagues studied six cannabis users with a clinical high-risk syndrome and six psychiatrically healthy cannabis users. Participants received active and placebo cannabis under randomized, double-blind conditions. Cognitive tasks and subjective effects were assessed before and after smoking.
The high-risk participants had attenuated symptoms assessed with structured clinical instruments. They should not be described as having an established psychotic disorder solely because they qualified for this study.
Which functions changed?
The high-risk group showed evidence of reduced response inhibition and more aversive intoxication after active cannabis relative to placebo. Psychomotor and cannabis-related attentional measures were also affected. The healthy comparison group did not exhibit the same significant pattern.
The groups were analyzed separately because of their size. A significant result in one group and a nonsignificant result in another is not, by itself, a statistically demonstrated difference between groups. That distinction limits claims about exactly how much additional vulnerability was established.
Clinical risk is not a concentration threshold
Participants were regular users, and some high-risk participants used antidepressants. Small samples, selected eligibility criteria, and coexisting symptoms restrict generalization. Laboratory task changes do not determine whether a particular person developed psychosis or committed an unsafe act.
When evaluating an opinion, separate the clinical history, documented exposure, observed symptoms, and tested cognitive function. This experiment supports further investigation of differential responses. It cannot convert a cannabis result into a psychiatric diagnosis or an individualized impairment finding.
Related reading: why cannabis effects can differ across memory tests.
Primary research
Sean P. Madden; John G. Keilp; Olivia Wu; Cheryl M. Corcoran; Ragy R. Girgis; Nehal P. Vadhan. Smoked Cannabis Effects in Cannabis Users at Clinical High-Risk for Psychosis: A Further Investigation of Cognition and Reward. Cannabis (2022). DOI: 10.26828/cannabis/2022.01.003.
