Cannabis Changed Response Timing More Consistently Than Serial-Addition Accuracy

forensic toxicology working group members October 31, 2026 Forensic Toxicology

In this acute cannabis experiment, slowing on a serial-addition task appeared across more tested conditions than a significant reduction in the total correct. Response latency and accuracy should therefore be reported separately.

The task combined attention and calculation

Participants viewed a sequence of single-digit numbers and selected the sum of the two most recently presented numbers. Although named the Paced Auditory Serial Addition Task, the computerized version described in this report used numbers displayed on a screen.

The study assessed total correct across ninety trials and reaction times for responses. Seventeen adults with no cannabis use in the preceding month received placebo, 10 mg THC and 25 mg THC through smoked and vaporized cannabis sessions.

Slower correct responses did not imply every accuracy comparison was significant

The report describes peak reaction time for correct responses slowing by at least 120 milliseconds relative to placebo at both active doses and inhalation methods. In contrast, its summary of significant total-correct reductions identified the 25 mg vaporized condition.

This pattern would be obscured by calling the task simply “positive” or “negative.” An accuracy result without its latency measure could underdescribe performance; a latency result should not be rewritten as a significant accuracy deficit in every condition.

Limits on individual conclusions

These are group comparisons on a trained laboratory task, not a diagnosis of a particular person’s ability to drive or perform every calculation. The sample was small and used cannabis infrequently. The companion pharmacokinetic publication reports the same experiment, and the published correction clarifies the peak-change table title.