Mokrysz, C; (2017) Acute and non-acute effects of cannabis in adolescents and adults. Doctoral thesis , UCL (University College London).

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Abstract

Preclinical research demonstrates that cannabinoids have differing effects in adolescent and adult animals, and human epidemiological research suggests that adolescent cannabis use has greater potential for harm than adult use. In chapters 1 and 2, I review this literature, describing the acute and non-acute effects of cannabis on memory, response inhibition and psychotic-like symptoms, with a focus on findings relating to adolescent populations and age of cannabis use onset. In chapter 3, I describe associations between adolescent cannabis use, IQ and educational performance, demonstrating that adjustment for potential confounders – most notably cigarette use – leaves cannabis use not associated with lower performance. In chapter 4, I describe the first study to compare the acute effects of cannabis in human adolescent (n=20; 16-17 years old) and adult (n=20; 24-28 years old) male cannabis users, in a placebo-controlled, double-blind cross-over design. After inhaling vaporised active or placebo cannabis, participants completed tasks assessing memory, inhibition, alongside physiological measures and subjective drug effects (e.g. “stoned”). Results showed contrasting profiles of adolescent resilience (blunted subjective, physiological and memory effects) and vulnerability (lack of satiety, impaired inhibitory processes). In chapter 5, in the same sample, I describe the acute psychotic-like effects of cannabis. Cannabis increased psychotic-like symptoms and the incidence of speech illusions in both adolescents and adults, though some self-rated effects were heightened in adults. In chapter 6, in a reduced sample, I describe the acute effects of cannabis on anhedonia (as indexed by reward responsivity, hedonic capacity and self-rated anhedonia) in adolescents (n=13) and adults (n=13). Cannabis did not affect reward responsivity or hedonic capacity in either group, though adults but not adolescents reported self-rated increases in anhedonia. In chapter 7, I integrate my findings, discuss their implications, consider limitations and suggest directions for future research into the effects of cannabis use in adolescence.

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