CBD and Schizophrenia Cognition: Why the Multiple-Testing Threshold Matters

forensic toxicology working group members October 28, 2026 Forensic Toxicology

A CBD–amisulpride trial reported nominal cognitive improvements, but the paper’s stated multiple-testing threshold was much stricter than p = 0.05. The results should not be summarized from the title alone.

An exploratory secondary analysis

Forty-two patients with acute schizophrenia were randomized to CBD or amisulpride for four weeks. Cognition was a secondary objective. Twenty-nine completed two cognitive assessments, and fewer completed every test.

This was an active-controlled comparison, not a placebo-controlled test of cognitive benefit. Improvement over time could include effects of clinical recovery, repeated testing and the inpatient setting.

Nominal significance and corrected significance

The authors specified that Bonferroni correction would require p below 0.0004. Reported within-group p-values for improvements such as visual memory and processing speed were above that threshold, even when below 0.05.

These findings can be described as exploratory signals with effect-size estimates. They should not be presented as all meeting the paper’s corrected criterion. The study also found no post-treatment cognitive differences between groups.

No difference does not prove equivalence

Failing to detect a difference in a small study is not a formal equivalence demonstration. Wide uncertainty and incomplete outcome data can conceal clinically meaningful differences.

Likewise, no relevant correlation with symptom changes or serum anandamide does not prove that every possible mechanism is independent of those variables. Absence of a detected correlation and proof of no causal pathway are different propositions.

The useful scientific question is which cognitive endpoint, analysis set and significance standard supports a claim. This trial cannot establish a general cognitive-enhancement effect of CBD or certify functional recovery in a particular patient.