Cannabis reliably increased psychotic-like symptoms but CBD did not blunt the effect | Research

The takeaway

Two double-blind placebo-controlled studies found inhaled cannabis reliably increased psychotic-like symptoms and may increase speech illusions, but CBD in the cannabis did not reduce these effects, and adolescents were not more vulnerable than adults.

Psychosis researchers, cannabis consumers, and anyone interested in CBD's interaction with THC-related psychiatric effects.

CBD did not blunt THC-induced psychotic-like symptoms

What the researchers found

Cannabis increased psychotic-like symptoms (PSI scores) in both studies. In Study 2, cannabis increased the odds of speech illusion 3.1 times. Cannabis with CBD showed no difference from cannabis without CBD on psychotic outcomes (Study 1). Adults showed more psychotic-like symptoms than adolescents (Study 2), contrary to the hypothesis that adolescents would be more vulnerable.

Why it matters

The assumption that CBD protects against THC-induced psychotic effects has influenced cannabis product development and regulation. This study challenges that assumption in a controlled acute dosing paradigm.

The numbers in context

Study 1: 17 adults, no CBD protection; Study 2: 20 adolescents + 20 adults; speech illusion OR 3.1 (95% CI 1.3-7.2); adults showed more psychotic-like symptoms than adolescents

How the study worked

Two double-blind placebo-controlled studies. Study 1 compared cannabis with CBD vs without CBD in 17 adults. Study 2 compared cannabis effects in 20 adolescents vs 20 adults. All participants were healthy current cannabis users. Outcomes included Psychotomimetic States Inventory and speech illusion in a white noise task.

What this study cannot tell us

Very small samples (17 and 40 participants). Single acute dose may not reflect chronic use patterns. Only healthy current cannabis users were tested, excluding the most vulnerable individuals.

How to read the evidence

Double-blind placebo-controlled design with rigorous methodology, but very small sample sizes limit statistical power.

When this study was published

Published in 2021.

The bigger picture

These findings challenge two popular assumptions: that CBD blunts THC's psychotic effects and that adolescents are acutely more vulnerable. However, acute effects may differ from chronic exposure patterns that contribute to long-term psychosis risk.

Questions still open

Would CBD protection emerge with repeated dosing rather than acute administration? Why were adults more susceptible to acute psychotic effects than adolescents? How do these acute findings relate to the epidemiological association between adolescent cannabis use and psychosis risk?

Common questions

Does CBD protect against THC-induced psychotic effects?

Not in this study. Cannabis with CBD showed no difference from cannabis without CBD on psychotic-like symptoms or speech illusion in a controlled acute dosing study of 17 adults.

Are teenagers more vulnerable to psychotic effects of cannabis?

Surprisingly, no in this acute study. Adults actually showed more psychotic-like symptoms than adolescents. However, long-term risk from repeated adolescent use may still differ.

Read the original research

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

Psychological medicine, 51(12), 2134-2142

View on PubMed ↗Publisher’s paper ↗

Citation

Mokrysz, Claire; Shaban, Natacha D C; Freeman, Tom P; Lawn, Will; Pope, Rebecca A; Hindocha, Chandni; Freeman, Abigail; Wall, Matthew B; Bloomfield, Michael A P; Morgan, Celia J A; Nutt, David J; Curran, H Valerie. (2021). Acute effects of cannabis on speech illusions and psychotic-like symptoms: two studies testing the moderating effects of cannabidiol and adolescence.. Psychological medicine, 51(12), 2134-2142. https://doi.org/10.1017/S0033291720001038