Blinding Guesses Were Measured at Defined Points in the Cannabis Challenge

The trial assessed treatment guesses before and after the cannabis challenge sequence. Those measurements supplied evidence about blinding without proving that every participant remained unaware throughout the experiment.

The report gave the counts

Before THC during the first experiment, participants correctly guessed CBD-versus-placebo pretreatment on sixteen of thirty occasions. At the end of the second experiment, they were correct on fourteen of thirty occasions. Researchers assessed at that second time point were correct on five of thirty occasions. The paper also reported a blinding index.

A guess is a time-specific observation

A correct guess can arise by chance, while an incorrect one does not establish perfect masking. Timing matters because experiences during the session may influence later beliefs. The counts should not be presented as a diagnosis of which individual knew their assignment, or as proof that expectations caused the clinical and cognitive findings.

Use masking evidence alongside the design

CBD and placebo capsules were matched in appearance, and allocation was concealed from participants and researchers. The small crossover experiment still required outcome-specific interpretation. Its delayed-recall and symptom findings cannot be dismissed solely because some guesses were correct, nor converted into universally blinded effects without retaining the reported assessment points.

Related analysis: the schizophrenia cannabis-challenge findings.

Research cited

Chesney and colleagues (2025). Does cannabidiol reduce the adverse effects of cannabis in schizophrenia? A randomised, double-blind, cross-over trial. DOI: 10.1038/s41386-025-02175-3.