Vaporized THC Affected Both Speed and Accuracy on a Digit-Symbol Task

forensic toxicology working group members October 31, 2026 Forensic Toxicology

Vaporized cannabis reduced more than the number of completed responses on a digit-symbol task: accuracy also declined in the tested conditions. The separate endpoints help distinguish slower output from less accurate work.

What participants actually did

Seventeen healthy adults with no cannabis use in the preceding month completed sessions with smoked or vaporized cannabis containing 0, 10 or 25 mg THC. On the computerized Digit Symbol Substitution Task, they reproduced displayed patterns using a keyboard during a 90-second period.

The investigators measured patterns attempted, patterns correct and percentage correct. Those are related outcomes, but fewer correct responses alone would not reveal whether a participant worked more slowly, made more errors, or both.

The vaporized conditions changed several endpoints

Both active vaporized doses significantly reduced attempts, correct responses and percentage correct relative to placebo under the reported planned comparisons. This pattern does not support explaining the reduced correct total solely as deliberate slowing while preserving accuracy.

It also does not mean every comparison involving smoked cannabis or every cognitive task was significant. The result belongs to these endpoints, doses and administration conditions rather than an undifferentiated statement that all performance deteriorated equally.

Applying the task result carefully

Keyboard pattern reproduction is a laboratory performance measure, not an observed crash or an individualized driving assessment. The small infrequent-user sample and particular vaporizer constrain generalization. The companion blood-and-saliva paper describes the same experiment, not another independent trial. The published correction clarified the table title identifying peak changes from baseline.