January 17, 2018
2 min read

Teenage cannabis, cigarette use may heighten risk for later psychosis

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Study findings showed that adolescents who use cannabis or tobacco are at increased risk for subsequent psychotic experiences; however, this association was greater among cannabis users.

“Individuals who use cannabis regularly have a 2- to 3-fold increased risk of a psychotic outcome. Tobacco use is also associated with an increased incidence of psychotic disorders in cohort studies, and (less consistently) with subclinical psychotic symptoms,” Hannah J. Jones, PhD, from the Centre for Academic Mental Health, Bristol Medical School, U.K., and colleagues wrote in JAMA Psychiatry. “As most people who use cannabis also smoke cigarettes, teasing out potentially causal effects of cannabis from those of tobacco is difficult, particularly as individuals usually mix their cannabis with tobacco, even when classing themselves as nonsmokers.”

In their analysis, researchers conducted a latent class analysis to identify subgroups of individuals according to similar patterns of cigarette and cannabis use behavior to analyze the relationship between different classes and future psychotic experiences, compare confounding patterns across classes and determine whether childhood psychotic experiences are linked to teenage cannabis and cigarette use.

By conducting a semi-structured psychosis-like symptom interview, investigators assessed 12 psychotic experiences — including hallucinations, delusions and thought interference — among 14,062 children at age 12 and 18 years enrolled in a longitudinal cohort study. They collected measurements of cigarette and cannabis use at six time points between ages 14 and 19 years. Then, they examined whether psychotic experiences at age 12 years were associated with subsequent latent class membership, and whether the membership was associated with subsequent psychotic experiences at age 18 years, before and after adjusting for confounders.

The study included 5,300 participants who had at least three measures of cigarette and cannabis use from age 14 to 19 years. Before adjusting for confounders, adolescents in the early-onset cigarette-only use (4.3%), early-onset cannabis use (3.2%) and late-onset cannabis use (11.9%) latent classes were at higher risk for psychotic experiences compared with nonusers (65.9%; P < .001). After adjustment, the association for early-onset cigarette-only use weakened by about 60% (adjusted OR = 1.78; 95% CI, 0.54-5.88); in contrast, those for early-onset cannabis use (aOR = 3.7; 95% CI, 1.66-8.25) and late-onset cannabis use (aOR = 2.97; 95% CI, 1.63-5.4) stayed consistent. Comparison of the substance use classes showed strong evidence to rule out equivalence between the association of late-onset cannabis use and late-onset cigarette-only use with psychotic experiences (OR = 3.63; 95% CI, 1.12-11.76).

“Both early-onset and late-onset cannabis use classes were associated with psychotic experiences at age 18 years and were only minimally attenuated after adjusting for potential confounders,” Jones and colleagues wrote. “Associations observed between tobacco use and psychotic experiences are more likely than those for cannabis use to be influenced by other characteristics of people who develop psychotic experiences.” – by Savannah Demko

Disclosures: The authors report no relevant financial disclosures.