Short answer: Half-life is not a fixed number that can be applied without context. A systematic review of human CBD pharmacokinetics reported estimates ranging from hours to days depending on route, formulation, dosing pattern, and study design.
The researchers searched PubMed and Embase for human studies that administered CBD and reported at least one pharmacokinetic measurement. Twenty-four publications met the criteria. Routes included intravenous administration, oral capsules, drops and solutions, oromucosal spray, nebulization, aerosol, vaporization, and smoking.
Many studies were small. Some involved CBD alone, while others used CBD with THC or in a cannabis extract. Populations and formulations also differed, limiting direct comparisons.
The review reported half-life estimates of approximately 1.4 to 10.9 hours after oromucosal spray, about 24 hours after intravenous administration, roughly 31 hours after smoking, and two to five days after chronic oral administration.
Those numbers are not interchangeable. Repeated dosing can create accumulation and a longer apparent terminal phase. The sampling schedule also matters: if collection stops too early, the slow terminal decline may be missed.
Peak concentration and area under the concentration–time curve generally increased with dose. Inhaled or smoked CBD reached peak concentration faster than oral or oromucosal products. Fed conditions and lipid-based formulations increased peak concentration in the reviewed studies.
The authors found a reported smoking bioavailability of 31%, but noted that absolute bioavailability had not been adequately reported for most other human routes despite the availability of intravenous data.
A detected CBD concentration cannot be interpreted from dose alone. Relevant questions include the product, route, formulation, food intake, acute versus repeated use, timing of the sample, co-administered THC, and the assay’s measured analytes.
A half-life estimate from chronic oral dosing should not be used as though it described a single inhaled exposure. Nor does a long terminal half-life mean that subjective effects or impairment persist for the entire elimination period.
The literature was sparse and heterogeneous. The review could summarize patterns but could not perform robust pooled statistical analysis. Its most defensible conclusion was that CBD pharmacokinetics are formulation- and context-dependent, and better controlled human studies are needed.
Source: Millar SA et al. PubMed record (PMID 30534073); full review DOI.