Bioavailability and format

Bioavailability is the fraction of a dose that reaches systemic circulation unchanged. Intravenous delivery is 100% by definition. Everything else is less.

For anything swallowed, the main loss is first-pass metabolism. CBD absorbed through the gut travels to the liver before it reaches general circulation, and liver enzymes, chiefly CYP3A4 and CYP2C19, metabolise a large fraction of it on the way through. What survives is what acts.

Swallowed products, meaning capsules, gummies and edibles, run at roughly 6% to 19% bioavailability. Onset is 45 to 120 minutes because the product has to be digested first. The effect lasts longest, commonly 6 to 8 hours, because absorption is gradual. A 25 mg gummy delivering 6% puts about 1.5 mg into circulation. At 19% it is closer to 4.75 mg. Same gummy, same person, different meal.

Sublingual tinctures held under the tongue absorb partly through the mucous membrane, entering the bloodstream directly and skipping the first liver pass for that portion. Estimates run from 12% to 35%. Onset is 15 to 45 minutes and duration 4 to 6 hours. The critical detail is that most people swallow too early. Sixty to ninety seconds under the tongue is the difference between sublingual and oral delivery, and swallowing at ten seconds gives you an expensive edible.

Inhaled products reach 30% or more, with onset in minutes and duration of 2 to 3 hours. Fastest and shortest.

Topicals are a different question. Cannabinoids applied to skin interact with local cannabinoid receptors in the tissue and do not reach the bloodstream in meaningful quantity. Bioavailability in the systemic sense is close to zero, which is not a failure of the product. A topical is targeting a knee, not the whole body, and it will not show up on a drug test for the same reason.

CBD is lipophilic. It dissolves in fat, not water, and how much fat is present when you take it changes absorption substantially.

Research on Epidiolex, the FDA-approved CBD medication, found that taking it with a high-fat meal raised peak plasma concentration and total exposure several-fold compared with fasting. Later work has consistently pointed the same direction.

Take oral CBD with food, and food containing fat. Yoghurt, nuts, avocado, cheese, a meal with oil in it. Taking the same capsule on an empty stomach and with a fatty meal can produce a several-fold difference in what reaches circulation, which is a larger effect than moving one step up in product strength.

This is also why the carrier oil in a tincture matters. MCT oil is the most common because medium-chain triglycerides absorb readily. Hemp seed oil, olive oil and others behave slightly differently, and the difference between carriers is smaller than the difference between taking it with food or without.

A 25 mg gummy and a 25 mg tincture dose are not the same dose. The tincture, used correctly, delivers roughly twice as much to circulation.

When someone switches formats and reports the new product is weaker, this is usually why, and the product is often fine. If you are moving from a tincture to gummies, expect to need a higher labelled milligram figure for a comparable effect, and expect a slower onset and a longer tail.

Nano and water-soluble products are the industry's answer to this. Emulsifying CBD into very small droplets does improve absorption, and the size of the improvement is frequently overstated on packaging. Ask for the data behind a bioavailability claim; a brand that has actually measured it will have something to show you.

Pick the format for the timing you need. Tincture for something you want inside an hour and can control precisely. Gummy or capsule for all-day coverage and convenience. Topical for one specific joint or muscle.

Then take it with fat, hold tinctures under the tongue for a full minute, and keep the format constant while you are finding your dose. Changing two variables at once tells you nothing about either.