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Acute effects of cannabis on speech illusions and psychotic-like symptoms: two studies testing the moderating effects of cannabidiol and adolescence

  • Claire Mokrysz (a1), Natacha D. C. Shaban (a1), Tom P. Freeman (a1) (a2) (a3), Will Lawn (a1), Rebecca A. Pope (a1), Chandni Hindocha (a1), Abigail Freeman (a1), Matthew B. Wall (a1) (a4) (a5), Michael A. P. Bloomfield (a1) (a6) (a7) (a8), Celia J. A. Morgan (a1) (a9), David J. Nutt (a10) and H. Valerie Curran (a1)...



Acute cannabis administration can produce transient psychotic-like effects in healthy individuals. However, the mechanisms through which this occurs and which factors predict vulnerability remain unclear. We investigate whether cannabis inhalation leads to psychotic-like symptoms and speech illusion; and whether cannabidiol (CBD) blunts such effects (study 1) and adolescence heightens such effects (study 2).


Two double-blind placebo-controlled studies, assessing speech illusion in a white noise task, and psychotic-like symptoms on the Psychotomimetic States Inventory (PSI). Study 1 compared effects of Cann-CBD (cannabis containing Δ-9-tetrahydrocannabinol (THC) and negligible levels of CBD) with Cann+CBD (cannabis containing THC and CBD) in 17 adults. Study 2 compared effects of Cann-CBD in 20 adolescents and 20 adults. All participants were healthy individuals who currently used cannabis.


In study 1, relative to placebo, both Cann-CBD and Cann+CBD increased PSI scores but not speech illusion. No differences between Cann-CBD and Cann+CBD emerged. In study 2, relative to placebo, Cann-CBD increased PSI scores and incidence of speech illusion, with the odds of experiencing speech illusion 3.1 (95% CIs 1.3–7.2) times higher after Cann-CBD. No age group differences were found for speech illusion, but adults showed heightened effects on the PSI.


Inhalation of cannabis reliably increases psychotic-like symptoms in healthy cannabis users and may increase the incidence of speech illusion. CBD did not influence psychotic-like effects of cannabis. Adolescents may be less vulnerable to acute psychotic-like effects of cannabis than adults.


Corresponding author

Author for correspondence: Claire Mokrysz, E-mail:


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Acute effects of cannabis on speech illusions and psychotic-like symptoms: two studies testing the moderating effects of cannabidiol and adolescence

  • Claire Mokrysz (a1), Natacha D. C. Shaban (a1), Tom P. Freeman (a1) (a2) (a3), Will Lawn (a1), Rebecca A. Pope (a1), Chandni Hindocha (a1), Abigail Freeman (a1), Matthew B. Wall (a1) (a4) (a5), Michael A. P. Bloomfield (a1) (a6) (a7) (a8), Celia J. A. Morgan (a1) (a9), David J. Nutt (a10) and H. Valerie Curran (a1)...


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