Weighed Cannabis Was Not the Same as a Model-Estimated Inhaled THC Dose
Subtracting cannabis product weight before and after use does not directly measure how much THC entered a person’s circulation. A population pharmacokinetic study used repeated blood samples to estimate inhaled dose and found that the estimate depended on use-pattern information.
Observed concentrations informed a model
Investigators studied 29 participants using high-potency flower or concentrates ad libitum during a 15-minute session. Frequent blood samples were obtained over approximately 135 minutes, supporting a three-compartment model of THC disposition.
The measured blood concentrations and the model-estimated dose are different quantities. The latter depends on the model structure, its assumptions and the information supplied to it. It is not another direct laboratory measurement of the consumed product.
Product content could overstate delivered exposure
Occasional users had lower model-estimated inhaled THC doses than daily users after covariate adjustment. Simple product-weight calculations did not adequately explain the high variability in concentrations among people using similar material.
The model did not identify a significant difference in its three-compartment pharmacokinetics across the analyzed user groups. That finding does not mean that inhalation behavior, delivered exposure or functional responses were identical.
Limits on reconstructing an unknown event
The analysis relied on early, closely timed samples and a witnessed use session. An isolated blood draw hours after an unknown exposure does not contain the same information. Extrapolating an individual dose from that isolated result would require additional validation.
Model-estimated exposure also does not supply a measured impairment curve. A forensic report should separate product weight, labeled potency, absorbed dose estimates and observed performance. The study improves understanding of exposure estimation under defined conditions without turning any one of those quantities into a substitute for the others.
Related: Interpreting cannabinoid concentrations and functional effects.
Primary research
Dose Estimation Utility in a Population Pharmacokinetic Analysis of Inhaled Δ9-Tetrahydrocannabinol Cannabis Market Products in Occasional and Daily Users. Therapeutic Drug Monitoring (2024).
