Postmortem Cannabis Testing: A Validated Extraction Does Not Reconstruct Life Before Death
A method that successfully extracts THC from postmortem specimens establishes analytical capability. It does not independently establish how the deceased behaved before death or whether cannabis caused an accident.
What the laboratory developed
Researchers developed a liquid–liquid extraction and gas chromatography–mass spectrometry method for THC and THC-COOH, applying it to 41 postmortem samples. The workflow used separate extraction conditions for parent THC and its carboxy metabolite, with derivatization for the latter.
This was human-specimen analytical research, not controlled dosing of living participants. The study assessed detection, calibration, precision, accuracy and recovery. Those endpoints address measurement performance rather than functional impairment.
The exact matrix still matters
Although the paper describes postmortem blood, its preparation section states that plasma was separated by centrifugation when possible. That qualification matters when evaluating a result attributed simply to “blood.” Whole blood and separated plasma are different preparations and should be identified accurately in a case report.
The authors discuss practical difficulties with degraded postmortem samples, including problems passing material through solid-phase extraction cartridges. A method’s practical usefulness in that setting does not eliminate specimen heterogeneity.
Validation is not a causal experiment
The method showed acceptable analytical precision and accuracy under its validation conditions. The case application demonstrated that the workflow could be used on actual submissions. It did not validate a conversion from a postmortem concentration to a living person’s earlier concentration or performance.
THC and THC-COOH must also remain separate: parent drug and an inactive carboxy metabolite do not answer the same toxicological question. The presence of either requires interpretation with collection site, timing, preparation and other case evidence.
Questions an opinion should answer
Ask which specimen was actually extracted, whether the laboratory’s own validation covers its condition, and which inference the analyst proposes. An accurate concentration can support exposure evidence while leaving impairment, timing and cause of death unresolved. Analytical success should not be used to fill those evidentiary gaps.
For context, see our discussion of THC concentrations and the separate question of impairment.
Primary research
Ivan Álvarez-Freire and colleagues. Simple Method for the Determination of THC and THC-COOH in Human Postmortem Blood Samples by Gas Chromatography—Mass Spectrometry. Molecules (2023). DOI: 10.3390/molecules28083586.
