When CBD and THC were co-administered by vaporization, high-dose CBD significantly decreased the systemic availability of THC, with frequent cannabis users showing higher availability of both compounds.
Medical cannabis prescribers, pharmacologists, and patients using combination THC:CBD products.
High-dose CBD significantly decreased THC systemic availability when co-inhaled
What the researchers found
In a randomized, double-blind, crossover study, concomitant inhalation of high-dose CBD significantly decreased the systemic availability of THC. Population pharmacokinetic models showed that frequent cannabis users had higher systemic availability of both THC and CBD compared to infrequent users.
Why it matters
Many medical cannabis users consume both THC and CBD. Understanding how they interact pharmacokinetically is essential for dosing guidance. The finding that CBD reduces THC availability could explain why CBD-rich products feel less intoxicating.
The numbers in context
High-dose CBD significantly decreased THC systemic availability. Frequent users had higher availability of both compounds. Population PK models developed for both THC and CBD.
How the study worked
Randomized, double-blind, crossover, placebo-controlled design. THC and/or CBD in ethanol were vaporized and inhaled. Plasma concentrations analyzed and population pharmacokinetic models developed by pooling with published data.
What this study cannot tell us
Relatively small sample; vaporized administration only (results may differ for oral or sublingual routes); pooled data from different studies for PK modeling; acute dosing only.
How to read the evidence
Moderate: randomized, double-blind crossover design with PK modeling, though sample size was limited.
When this study was published
Published 2020.
The bigger picture
This finding has practical implications: adding CBD to THC products may actually reduce THC exposure, not just modulate its effects subjectively. This could inform product design and dosing recommendations for medical cannabis.
Questions still open
- Does the CBD-THC interaction hold for oral administration? Should medical cannabis dosing account for CBD-mediated reduction in THC availability?
Common questions
Does CBD reduce the effects of THC?
Do frequent cannabis users absorb more THC?
Read the original research
Model-based analysis on systemic availability of co-administered cannabinoids after controlled vaporised administration.
Internal medicine journal, 50(7), 846-853
Citation
Liu, Zheng; Galettis, Peter; Broyd, Samantha J; van Hell, Hendrika; Greenwood, Lisa-Marie; de Krey, Peter; Steigler, Amy; Zhu, Xiao; Schneider, Jennifer; Solowij, Nadia; Martin, Jennifer H. (2020). Model-based analysis on systemic availability of co-administered cannabinoids after controlled vaporised administration.. Internal medicine journal, 50(7), 846-853. https://doi.org/10.1111/imj.14415
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