Breath THC Half-Life Estimates Changed With the Sampling Interval
The reported breath THC half-life was much shorter immediately after smoking than at later sampling intervals. A two-point breath estimate was not a fixed whole-body elimination half-life.
Different portions of the decline produced different values
The report gave an average estimate of approximately 4.2 minutes over the zero-to-twenty-minute interval, compared with approximately 35 minutes over sixty-to-eighty minutes. The later value came from only six participants and had substantial variability. Sampling schedules and analyzable subsets differed across intervals.
The estimate belongs to the measured signal
A short decline in breath can reflect the dynamics of material recovered in exhaled samples. It should not be equated with the terminal half-life of THC in blood or tissues. Nor does a short calculated value alone establish the exact time of smoking or when functional effects end. The paper’s broader classification used additional parameters.
A new device needs its own validation
The authors developed a recent-inhalation approach in a selected smoking cohort, with self-reported impairment and disclosed commercial interests. The findings do not establish a universal decision rule for all products or users. A defensible interpretation retains the two collection times, signal definition and applicable uncertainty rather than quoting one half-life as a biological constant.
Related analysis: the combined test’s validation limits.
Research cited
DeGregorio and colleagues (2021). A comprehensive breath test that confirms recent use of inhaled cannabis within the impairment window. DOI: 10.1038/s41598-021-02137-x.
