Cannabis users have higher premorbid IQ than other patients with first onset psychosis

Abstract

a b s t r a c t a r t i c l e i n f oBackground: A number of studies have reported that patients with psychosis who use cannabis have better cognitive performance than those who do not. This is surprising as cannabis can impair cognition in healthy subjects. An obvious question is whether the better current performance of psychotic patients who have used cannabis is a reflection of their having a higher premorbid IQ than those psychotic patients who haven't used cannabis. Aim: In a sample of patients at their first episode of psychosis, we tested the hypothesis that patients who smoked cannabis would have a higher premorbid IQ than patients who did not. Methodology: 279 participants (119 patients and 160 healthy controls) were assessed in order to obtain current and premorbid IQ measures and detailed information on cannabis use. We examined the association between cannabis use and both premorbid and current IQ in patients and controls. Results: Patients who had ever smoked cannabis had significantly higher current (p b .001) and premorbid IQ (p = .004) compared to patients who had never used cannabis. This difference was not found among controls. Conclusions: These findings suggest that the better cognitive performance of patients with their first episode of psychosis who have used cannabis compared with those who haven't is due to the better premorbid IQ of the former.

Cognitive reserve and neuropsychiatric disorders

“…Cannabis users have an earlier age of onset of psychosis than nonusers. However they also have a higher premorbid IQ than those without a history of cannabis use [47][48][49]. These findings indicate that cannabis use may be a precipitating factor in the development of psychosis and that it counteracts the normally protective effect of cognitive reserve in delaying onset [47,50].…”

Gone to Pot – A Review of the Association between Cannabis and Psychosis

“…Emerging evidence, however, suggests that patients with cannabis use have higher premorbid IQ (247). The findings are not inconsistent with the experimental data; it is likely that persons who smoke cannabis have higher premorbid IQ, as evidenced by their ability to procure an illegal substance while evading the law.…”

Evaluating the relationship between cannabis use and IQ in youth and young adults at clinical high risk of psychosis

“…Another explanation is that early cannabis use may induce psychosis onset in less cognitively vulnerable individuals, i.e., those with better cognitive capacities, thereby facilitating the onset of psychosis that may otherwise not have occurred (Yucel et al, 2012). A related suggestion is that the better cognition in patients who use cannabis may have facilitated their recreational drug use like in typical adolescents (Ferraro et al, 2013). or that superior social skills enable cannabis-using patients to acquire and sustain a drug habit, which is reflected in their cognition (Potvin et al, 2008; Solowij and Michie, 2007).…”