CBD Bioavailability: What Human Studies Measured
Definition
Bioavailability is the share of an administered amount that reaches circulation, worked out by setting blood concentrations from one route against an intravenous reference that counts as 100% in circulation by definition [1]. In human data on cannabidiol, the oral figure reads low and variable, and precise values remain unestablished [1]. Route, formulation and trial conditions always travel with the number.
100% belongs to one route only
| Term | What the published human data records |
|---|---|
| Bioavailability | The share of an administered amount that turns up in circulation. It is worked out by setting blood concentrations from a given route against an intravenous reference, and that reference counts as 100% in circulation by definition [1]. |
| Oral cannabidiol in humans | The 2018 systematic review by Millar describes oral bioavailability as low and variable, and reports precise figures as unestablished [1]. Trial design, formulation and sampling differ from paper to paper, so the human record holds conditions rather than one clean percentage [1]. |
| What a figure is attached to | Any percentage is specific to the study and the formulation it was measured in. It is not a fixed property of the molecule that travels along with the word cannabidiol. |
| An incomplete statement | A bioavailability percentage given without route, without formulation and without the study behind it. Those three details are what make a number checkable. |
| The state of the human literature | Millar's 2018 review counts few studies and methods that are not standardised between trials, and finds no reliable single oral value in humans [1]. Cross-trial standardisation is still lacking [1]. |
| Why the intravenous arm matters | Every other route is read against it. Take that comparison away and there is no denominator left, so a percentage floats free of the measurement that produced it [1]. |
| What sits inside a reported range | Inter-individual differences, the sample size behind the mean and the analytical method used, all of them named in the human reviews [1][3]. |
| What the reviews deliver | Ranges, conditions and unresolved questions from published human data on cannabidiol pharmacokinetics [1]. Reading them means reading the conditions next to the numbers. |
First-pass metabolism, named in the 2018 review
| Point | Detail from the cited work |
|---|---|
| The main named factor | Hepatic first-pass metabolism is the reason Millar's 2018 systematic review gives for low oral figures in humans [1]. Swallowed cannabidiol passes liver metabolism before it reaches general circulation, and the review names that step as the principal one [1]. |
| The liver as the first column | Any discussion of swallowed cannabidiol starts there in the human pharmacokinetic record, before formulation questions come up at all [1]. |
| Why oral numbers scatter | Formulation, fed or fasted state, sampling times and analytical method all differ across the trials collected in 2018, so the values spread out instead of converging [1]. |
| What the review does not supply | A reliable single oral value in humans. The paper lists the number of studies as small and the methods as non-standardised [1]. |
| Oromucosal data in the same paper | Human oromucosal pharmacokinetic data were reviewed next to oral data in Millar's 2018 work, which is one reason the two routes get discussed together [1]. |
| Where variability is attributed | In Huestis's 2007 review of human cannabinoid pharmacokinetics, a large part of the spread is put down to study conditions and, for inhalation, to behaviour during use [3]. |
| Why the phrase low and variable survives | Across the human data gathered in 2018 it is the description that holds up, while a single tidy percentage does not [1]. |
| Commercial formats | The cited pharmacokinetic reviews contain no head-to-head comparison of product formats sold on a shelf [1]. Describing a delivery strategy is a description, not a demonstrated human outcome. |
| Four questions for any figure | Which route, which formulation, which trial, and how the blood was sampled. Answer those and a percentage becomes readable [1]. |
One meal, one trial, one measured difference
In 2018 Taylor and colleagues published a phase I trial in healthy participants. Randomised, double blind, placebo controlled. It ran single ascending doses, then multiple doses, and it included a food effect part. Healthy adults, controlled dosing, blood sampled to a schedule [2]. In that food part, highly purified cannabidiol taken with food produced increased plasma exposure compared with the fasted condition [2]. That is a pharmacokinetic observation: concentrations measured in blood, under the conditions the protocol set out.
Which is worth saying slowly. The comparison sat inside one trial, with one highly purified formulation and defined meals [2]. It does not carry an equivalence across every formulation or every meal composition, and it is not an instruction. The status of the finding is exactly that: measured concentrations, trial conditions [2]. Millar's 2018 review reaches a similar limit from the other side, with few studies, methods that differ and no single oral figure to quote [1].
Where the food-effect reading stops
Human pharmacokinetic reviews keep the routes apart for a reason. Swallowing, oromucosal contact and inhalation each show their own concentration-time profile, with different speeds of appearance in plasma and different amounts of measurement variability [3]. Contact time and the fraction that ends up swallowed are listed as confounders on the oromucosal side [3]. So a food observation from a swallowed trial formulation stays where it was measured. We have been working with cannabinoids since 2014, and the in-house rule matches the reading rule here: a batch analysis tells you what is in the bottle, while a pharmacokinetic number belongs to the trial that produced it.
Three routes, three concentration-time profiles
| Route | What human data record | What stays open |
|---|---|---|
| Swallowed: oil by mouth, capsules | Oral bioavailability reads low and variable across the studies gathered by Millar in 2018, with hepatic first-pass metabolism named as the main factor [1]. | No single value in humans, because trial designs and formulations differ [1]. |
| Swallowed, fed against fasted | In Taylor's 2018 phase I trial, plasma exposure of highly purified cannabidiol was higher with food than in the fasted condition [2]. | One formulation and defined meals; no equivalence stated for other formulations or meals [2]. |
| Sublingual and oromucosal | Absorption across the mucous membranes of the mouth is described as a profile of its own, separate from swallowing [3]. Human oromucosal data were reviewed alongside oral data in 2018 [1]. | How much stays oromucosal in ordinary use is not settled; the swallowed fraction and contact time differences are named as confounders [3]. |
| Inhaled | Rapid appearance in plasma, with substantial variability attributed to inhalation behaviour and to study conditions [3]. | Behaviour-driven variability is hard to line up between trials [3]. |
| All three, side by side | Reviews of human data describe the administration profiles as distinct and not interchangeable [3]. | Cross-trial standardisation is still lacking in the published human literature [1]. |
| Commercial product formats | The cited reviews include no head-to-head comparison of formats sold to consumers [1]. | A format can share a route without sharing a measured figure [1]. |
| Inside every range | Inter-individual variability, sample size and analytical method are all part of what a reported range contains [1][3]. | Which is why ranges rather than round numbers are what the reviews hand over [1]. |
Frequently Asked Questions
4 questionsIs there a percentage for cannabidiol taken by mouth?
What is the 100% figure actually referring to?
Did the 2018 phase I trial compare different oils?
Why do sublingual figures come with so many caveats?
About this article
Luke Sholl has been writing about cannabinoids, CBD, and the broader benefits of nature since 2011. His background includes first-hand cannabis cultivation experience spanning the full seed-to-harvest lifecycle across so
This wiki article was drafted with AI assistance and reviewed by Luke Sholl, CBD & wellness writer. Editorial oversight by Joshua Askew.
Medical disclaimer. This content is for informational purposes only and does not constitute medical advice. Consult a qualified healthcare provider before use of any substance.
Last reviewed 27 серпня 2026 р.
References (3)
- [1]Millar, S.A. et al. (2018). A Systematic Review on the Pharmacokinetics of Cannabidiol in Humans. DOI: https://doi.org/10.3389/fphar.2018.01365
- [2]Taylor, L. et al. (2018). A Phase I, Randomized, Double-Blind, Placebo-Controlled, Single Ascending Dose, Multiple Dose, and Food Effect Trial of the Safety, Tolerability and Pharmacokinetics of Highly Purified Cannabidiol in Healthy Subjects. DOI: https://doi.org/10.1007/s40263-018-0578-5
- [3]Huestis, M.A. (2007). Human Cannabinoid Pharmacokinetics. DOI: https://doi.org/10.1002/cbdv.200790152
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