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.

Subclinical psychotic symptoms are present in the general population. Furthermore, they are quite common in diagnostic categories beyond psychosis, such as BPD patients.

We want to assess the differences between 3 groups: BPD (n = 68), FEP (n = 83) and controls (n = 203) in an experimental paradigm measuring the presence of speech illusions in white noise. The Positive and Negative Syndrome Scale was administered in the patient group, the Structured Interview for Schizotypy-Revised, and the Community Assessment of Psychic Experiences in the control and BPD group. The white noise task was also analysed within a signal detection theory (SDT) framework. Logistic regression analyses and the general linear models were used to analyse the adjusted differences between groups.

Differences were more prevalent in signals that were perceived as affectively salient in patients groups (9.6% in FEP vs 5.9% in BPD and 1% in controls; OR: 10.7; 95%CI: 2.2–51.6, p = 0.003 in FEP; OR: 6.3; 95%CI: 1.1–35.0, p = 0.036 in BPD). Besides, we found a worse general performance and more false alarms in the task for FEP group using SDT framework.

Experimental paradigms indexing the tendency to detect affectively salient signals in noise may be used to identify liability to psychosis in people with vulnerability. Its predictable value in other diagnostic categories and general population requires further research.