The CBD Excreted-Dose Calculation Used Volume and Molecular Weight
The study’s percentage of dose excreted was a calculated quantity using urine volume, analyte concentration and metabolite molecular-weight adjustment. It was not simply a urine concentration expressed as a percentage.
The calculation had several stages
For each collection, the investigators combined measured urine volume and concentration to estimate analyte amount. They summed amounts across collections, adjusting metabolites for molecular-weight differences, before relating the cumulative amount to the administered CBD dose. Pooled collections and the available observation period were part of that calculation.
Why concentration alone is insufficient
Two urine specimens can have different concentrations because of different volumes while containing similar analyte amounts. Metabolites also do not have the same molecular mass as parent CBD, so raw nanograms of each compound are not automatically interchangeable dose equivalents. The adjustment addresses that accounting issue; it does not independently measure pharmacological activity.
What the fraction cannot establish
Urinary recovery over the observed period does not account for every elimination route or prove absolute oral bioavailability. Neither does it provide a validated method to reconstruct an unknown dose from one urine specimen. The human study’s calculated fraction requires the collection information used to produce it and should remain distinct from blood exposure, clinical response and impairment.
Related analysis: the urinary CBD route comparison.
Research cited
Sholler and colleagues (2021). Urinary Pharmacokinetic Profile of Cannabidiol, THC and Their Metabolites following Oral and Vaporized CBD and Vaporized CBD-Dominant Cannabis Administration. DOI: 10.1093/jat/bkab059.
