Bioavailability

Bioavailability describes how much of a swallowed, inhaled or applied dose actually reaches systemic circulation. CBD is fat soluble and heavily metabolized by the liver on first pass, so oral bioavailability is low.

A 2018 systematic review of human pharmacokinetics found no direct measurement of oral bioavailability in humans. Animal studies cited there put it at roughly 13 to 19 percent, while the only absolute human figure came from smoking, at about 31 percent (Millar 2018). Inhaled routes reach peak concentration fastest. Oromucosal spray taken after a meal produced about 5 times the exposure of the same dose taken fasted.

Lipids explain much of that. Dietary fats and lipid-based excipients raise exposure to orally dosed cannabinoids by routing part of the dose through lymphatic absorption, which bypasses the liver (Zgair 2016). That is the rationale for MCT carriers, softgels with oil fills and nano-emulsions.

Minor cannabinoids follow similar patterns. A 2025 review found that pharmacokinetic values for CBD, CBG and CBC vary widely with dose, formulation, route and diet (Pharmaceutics 2025). Any fixed percentage printed on a label should trace to a study using that formulation.