Excluding Other Drug-Positive Participants Changed Some Vaporized-THC Cognitive Findings

In the prescribed-flower study, excluding participants with other positive drug-screen indications narrowed the set of significant cognitive findings. The sensitivity analysis changed which conclusions were most stable.

The full sample had several affected measures

Before exclusions, post-cannabis changes were reported for Trail Making A, Trail Making B, a Trail Making ratio and a Stroop measure. Other cognitive tasks were nonsignificant. The initial battery therefore did not support either uniform impairment or uniform absence of change.

The restricted analysis retained fewer findings

Eight participants had a positive indication for substances other than THC at one or more testing points. After excluding them, the Trail Making A and B findings remained, while the other comparisons were no longer significant. This pattern differs from the oral study, where excluding other drug-positive participants did not change the reported results.

Sensitivity analysis is not proof of confounding

The change does not establish that another drug caused a particular effect: reducing a sample also changes precision. Screening indications do not supply a complete exposure timeline. The appropriate account reports both analyses and identifies which findings persisted. This research used human cognitive tasks relevant to driving, not a direct demonstration of collision risk. A result’s stability across an exclusion analysis strengthens a specific inference without validating every broader claim about the entire battery.

Related analysis: the study’s main findings and limitations.

Research cited

Stefanidis and colleagues. Elucidating the acute effects of medically prescribed oral and vaporised delta-9-tetrahydrocannabinol on cognitive functions important for driving. Drug and Alcohol Review (2025). DOI: 10.1111/dar.14060.