Can CYP2C9 or CYP2C19 Genotyping Explain a Cannabis Blood Result?
A genotype may inform a metabolism hypothesis, but a small controlled-exposure analysis did not establish genotype-specific cannabis blood concentrations or a reliable last-use clock. Predicted enzyme activity and an observed cannabinoid result require separate interpretation.
What was analyzed?
Schulte and colleagues retrospectively examined samples from 27 people who had undergone controlled single and repeated vaporization of high-CBD, low-THC cannabis. They compared genotype-predicted CYP2C9 and CYP2C19 phenotypes with whole-blood cannabinoid concentrations and metabolic ratios.
This was human pharmacogenetic research involving a particular product profile and inhaled exposure. It was not a validation of a genetic test for impairment or of every oral and high-THC formulation.
The central null finding
The analysis found no statistically significant concentration or metabolic-ratio differences across predicted phenotypes. Some CYP2C9-related trends were consistent with earlier hypotheses, but the authors emphasize the small sample and retrospective design.
A trend should not be upgraded to an established individual prediction. Conversely, a nonsignificant result in this sample does not prove that genetic variability can never matter under other exposure conditions.
Predicted phenotype is not the whole metabolic state
Genotype-based categories estimate enzyme function. They do not capture every influence of medication interactions, illness, age, exposure timing, or actual absorbed dose. Similar concentrations can arise through different combinations of those factors.
The matrix here was whole blood. Parent THC, active 11-hydroxy-THC, inactive THC-COOH, and CBD are distinct analytes; a ratio involving one pair does not automatically reconstruct the timing or effect of the others.
Questions for an expert opinion
Ask which genetic variants were tested, how phenotype was assigned, whether the proposed inference has been validated for the actual product and route, and what uncertainty remains. Identify whether the claim concerns metabolism, exposure duration, or behavioral impairment.
This study supports further prospective investigation. It does not provide a genotype-based method to calculate a person’s dose, determine an exact consumption time, or classify an individual as impaired from a blood result.
For related context, see our discussion of interpreting THC blood concentrations.
Primary research
Janine Schulte; Leila Potzel; Priska Frei; Isabell Seibert; Kathrin Gerlach; Katja Mercer‑Chalmers‑Bender; Eva Scheurer; Henriette E. Meyer zu Schwabedissen; Iris Schulz. Assessing the influence of CYP2C9 and CYP2C19 genotypes on the metabolism of CBD-cannabis after controlled single and repetitive consumption. International Journal of Legal Medicine (2026). DOI: 10.1007/s00414-025-03708-7.
