CBD Bioavailability: Why the Number on the Label Isn't the Number You Get
If you swallow 33mg of CBD, considerably less than 33mg reaches your bloodstream. Published estimates of oral CBD bioavailability sit at roughly 6–13% — meaning most of what you take never makes it into circulation at all.
That is not a defect in the product. It is how the compound behaves in the body, and it is true of every oral CBD product on the market. But it explains a lot of things that otherwise look strange: why milligram comparisons between brands are less useful than they appear, why taking CBD with food changes the outcome, and why the delivery format is at least as important as the dose.
Our guide to CBD for focus and relaxation covers daily-use basics. This article is the mechanism underneath them.
What bioavailability means
Bioavailability is the proportion of a dose that reaches your bloodstream in a form your body can use.
Injected directly into a vein, a substance is 100% bioavailable by definition. Everything else is less, because everything else has to get past something first. For anything you swallow, that something is your digestive tract and then your liver.
The first-pass problem
When you swallow CBD, it is absorbed through the gut and travels to the liver before it reaches general circulation. The liver metabolises a substantial share of it on that first pass — converting CBD into metabolites, notably 7-hydroxy-cannabidiol, through cytochrome P450 enzymes.
Two consequences follow, and the second one is the one people miss.
First: most of an oral dose is metabolised before it can do anything, which is where the 6–13% figure comes from.
Second: that same enzyme system is why CBD interacts with medications. The liver enzymes that process CBD also process a long list of prescription drugs, and CBD can inhibit them. This is a genuinely important safety point rather than a technicality — see our article on CBD and prescription medication.
Bioavailability by route
| Route | Approximate bioavailability | Notes |
|---|---|---|
| Sublingual (held under tongue) | ~13–19% | Partly bypasses first-pass metabolism; some is still swallowed |
| Oral / swallowed (capsules, gummies, drinks) | ~6–13% | Full first-pass metabolism |
| Topical | Effectively negligible systemically | Acts locally in skin and tissue; not designed to reach the bloodstream |
These are ranges from the published literature, not precise constants — individual variation is large and formulation matters.
The sublingual advantage is real but partial. Holding oil under your tongue lets some of the dose absorb through the mucous membrane directly into the bloodstream; the rest gets swallowed and takes the ordinary route. That is why how long you hold it matters: 60 to 90 seconds is the practical target, and most people do not get close.
Why food changes the answer
CBD is fat-soluble. Taking it with food — particularly food containing fat — increases how much is absorbed, and this is one of the more consistent findings in the pharmacokinetics literature. Peak concentrations are higher in the fed state than the fasted state.
This has a straightforward practical implication. If you take CBD on an empty stomach some days and after dinner on others, you are effectively taking two different doses and then wondering why the results are inconsistent. Standardise the timing before you change the amount.
Why cross-brand milligram comparisons mislead
This is the part that is worth carrying into any purchase.
Two products both labelled 33mg per dose can deliver quite different amounts to your bloodstream depending on carrier oil, whether it is an emulsion, particle size, and whether the format is designed for sublingual use. A gummy and a tincture at the same milligram figure are not the same product.
So "more milligrams for less money" is not automatically better value, and a higher number on the label is not automatically a stronger product. What matters is how much arrives, and that is a function of format and how you use it.
What you can compare reliably is what a third-party lab measured. A certificate of analysis tells you what is actually in the bottle, which is the precondition for any of this mattering.
Getting more from what you take
Four things, in order of impact:
- Hold it sublingually for 60–90 seconds. The single biggest controllable difference between the sublingual and oral figures above.
- Take it with food containing fat. Consistently, at the same point in your day.
- Be consistent for at least two weeks. CBD accumulates in fat tissue with repeated dosing; a single dose is not representative.
- Change one variable at a time. Timing, then food, then amount — in that order.
What this means for our products
Comfort Drops and Sleepy Drops are formulated for sublingual use, which is why the instruction is to hold before swallowing rather than to drink it. If you swallow immediately, you have converted a sublingual product into an oral one and taken the lower bioavailability route.
Ice Hot Roll-On is a topical, and topical systemic absorption is negligible by design. That is the point — it acts where you put it. Comparing its milligram figure to a tincture's is comparing two different jobs.
Pet Drops are usually mixed into food in practice, which means the oral route and the oral timeline. That is fine; it is just worth knowing that "in food" and "under the tongue" are different, and dosing guidance assumes the realistic one.
Frequently asked questions
Does higher bioavailability mean I should take less? It means the delivery route matters as much as the number. Follow the product's dosing guidance rather than trying to compute a correction.
Are nanoemulsion or "water-soluble" CBD products more bioavailable? Formulation research is active and some approaches do improve absorption in studies. Treat specific marketing figures sceptically unless the brand can point to data on their product.
Why do I feel it more some days than others? Food, timing, how long you held it, how long you have been taking it, and ordinary day-to-day variation. Standardising the first three removes most of the noise.
Does bioavailability change the safety picture? It is part of it. Because CBD is metabolised by cytochrome P450 enzymes, anything that changes how much reaches your system is relevant if you take other medication. Talk to your pharmacist.
Sources
- Millar SA, et al. A Systematic Review on the Pharmacokinetics of Cannabidiol in Humans. Frontiers in Pharmacology, 2018. https://pmc.ncbi.nlm.nih.gov/articles/PMC6275223/
- Pharmacokinetics of Cannabidiol: A Systematic Review and Meta-Regression Analysis. Cannabis and Cannabinoid Research, 2024. https://pubmed.ncbi.nlm.nih.gov/37643301/
- Cannabidiol in Dietary Supplements: Characteristics, Routes of Administration, Bioavailability. Molecules, 2026. https://pubmed.ncbi.nlm.nih.gov/42451752/
- Cytochrome P450–Catalyzed Metabolism of Cannabidiol to the Active Metabolite 7-Hydroxy-Cannabidiol. https://pmc.ncbi.nlm.nih.gov/articles/PMC11025033/
- Evaluation of Cytochrome P450-Mediated Cannabinoid-Drug Interactions in Healthy Adult Participants. Clinical Pharmacology & Therapeutics, 2023. https://pubmed.ncbi.nlm.nih.gov/37313955/
This article is for general information and is not medical advice. CBD is not approved by the FDA to diagnose, treat, cure or prevent any disease. Talk to your healthcare provider before using CBD, particularly if you take prescription medication.