2021 Internationa Joural of Drug Policy
However, comparing products based on physical equivalencies or THC ‘content’ has limitations, in part because physical equivalency depends on the production method, form of supply, and the THC/CBD yield. More importantly, the mode of administration changes a drug’s pharmacokinetics (Grotenhermen, 2003; MA, 2007). For example, not all the THC in dried herb products is actively inhaled—much of it is released in the smoke between puffs—and not all the THC that is inhaled is absorbed. Recent research suggests potentially greater bioavailability of THC from dried herb that is vapourized versus smoked (Spindle et al., 2018). Studies estimate that approximately 20% of THC content in dried herb is metabolised and absorbed into the blood stream, compared to approximately 10% of that in edibles. The latter depends on a number of other factors, such as the presence of other foods in the stomach. The time to onset and duration of effect also differs: smoke inhalation and THC absorption into the bloodstream via the lungs produces faster, higher-peak effects; however, THC levels also abate more quickly. In contrast, oral ingestion leads to slower onset and longer duration, as well as higher concentrations of 11-OH-THC, a THC metabolite that crosses the blood-brain barrier more easily, producing greater psychoactive effects (Huestis, Henningfield, & Cone, 1992; Law, Mason, Moffat, Gleadle, & King, 1984; Nahas, 1975; Nadulski et al., 2005).
