Baseline Saliva THC Did Not Account for All Trail-Making Changes After Prescribed Cannabis

forensic toxicology working group members October 31, 2026 Forensic Toxicology

Trail Making B worsened after cannabis in both baseline THC-positive and baseline THC-negative subgroups. A positive predose oral-fluid screen therefore did not uniquely explain that finding.

The investigators examined baseline status separately

Many participants had THC-positive oral-fluid indications at the start of their appointments. The researchers divided the oral and flower samples by that baseline status to explore whether cognitive changes were limited to one group. These were secondary analyses, not randomized allocation to a saliva result.

The principal finding persisted across the split

In both studies, Trail Making B performance deteriorated in the positive and negative baseline subgroups. Other outcomes were less consistent across these smaller analyses. The result supports retaining the specific task finding rather than dismissing it solely because some participants already screened positive.

The screen still did not define a biological zero

A negative oral-fluid result is not proof of no residual drug anywhere in the body. A positive indication also does not quantify the participant’s impairment. Stratification cannot isolate tolerance, symptom relief or all differences in exposure history. The useful conclusion is about robustness of the measured change across the reported classifications. It does not establish that the subgroups had identical cannabinoid exposure, that saliva status is irrelevant to every task or that the test supplies a universal threshold for safe performance.

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