The interaction trial tested THC/CBD spray after a course of the interacting medication. It did not merely combine two first doses and measure an immediate interaction.
The exposure sequence was deliberate
Healthy male volunteers received a single four-spray THC/CBD dose alone and with rifampicin, ketoconazole or omeprazole. The combination challenge occurred at the end of medication periods described as ten days for rifampicin, five for ketoconazole and six for omeprazole.
Participants were randomized to treatment sequences within three separate medication groups. The repeated exposure to the other drug was therefore part of the intervention, not background medication that could be omitted from the study description.
Timing affects the question being tested
An experiment after repeated medication administration does not establish the effect of a single accidental co-ingestion. Nor does it provide a time course for when an interaction begins or disappears after discontinuation. Those questions require observations that this comparison did not independently supply.
Retain the pharmacokinetic outcome
Rifampicin lowered measured cannabinoid exposure, ketoconazole increased it and omeprazole did not show a significant change under the tested conditions. These findings concern plasma THC, CBD and 11-hydroxy-THC after this product and schedule. They are not individual dose-adjustment instructions or a measured driving-impairment curve.
Related reading: interpreting proposed CBD mechanisms.
Research cited
Stott and colleagues (2013). A Phase I, open-label, randomized, crossover study in three parallel groups to evaluate the effect of Rifampicin, Ketoconazole, and Omeprazole on the pharmacokinetics of THC/CBD oromucosal spray in healthy volunteers. DOI: 10.1186/2193-1801-2-236.
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