An important concern for medical cannabis is the issue of bioavailability. Simply put, bioavailability refers to “the degree and rate at which an administered drug is absorbed by the body’s circulatory system, the systemic circulation.” Bioavailability is key. In essence it determines the basic efficacy of drugs, and while for many synthetic pharmaceuticals bioavailability is a simple matter, it is a little more complex for cannabis.
By definition, anything taken intravenously is 100% bioavailable, but of course there are no current intravenous formulations of medical cannabis. Understanding routes of administration is actually important in understanding bioavailability.
Cannabis medicines can be inhaled, consumed or applied. Respectively, this generally means smoking or vaping, eating edible preparations or pure oils, and rubbing salves or balms into the skin for transdermal effects.
Bioavailability is quite variable among these options. Inhaling cannabis has a relatively high degree of bioavailability. A 2005 study called ‘Pharmacokinetics of cannabinoids’ found smoked THC to have about 30% average bioavailability, but it’s much harder to dose control a smoked substance than it is a vaped substance with temperature controls. Smoking is also not clinically recommended due to respiratory harms.
A 2016 study called ‘Medicinal Cannabis: In Vitro Validation of Vaporizers for the Smoke-Free Inhalation of Cannabis’ identified that with the right vaporizer, bioavailability for THC and CBD can reach 50–80%.
Eating cannabis preparations of any number of types is also hugely variable. Cannabinoids are lipophilic and if they aren’t combined with a fatty substance on consumption, bioavailability will be significantly limited. Dose control is therefore also a tricky issue in edibles, where product variation becomes a concern as substance concentrations can be unevenly distributed among a single batch.
Most scientific studies still place edibles somewhere in the 4–20% bioavailability range, making them clearly less efficient than inhaled routes. Popular ‘carriers’, or the combined fatty oils that increase edible bioavailability include things like coconut oil.
Transdermal routes are not the most effective forms of administration, unless there is a localised dermatological or muscular issue. Topical applications will have little impact, if any, on internal medicine conditions.
High bioavailability is of course desirable. The higher the proportion of the active substances in a given dose, the less medication that will be required to treat symptoms or conditions. Refining vapourised methods of consuming cannabis, particularly with regards to chemical activation at precisely controlled temperatures, appears to be the most effective current avenue towards creating effective cannabis medicines.
In the medium term future, however, medical technology could unlock exciting potential in nanotechnology, notably via the synthetic binding of lipid nano-coatings around individual cannabinoid molecules, resulting in highly effective cannabinoid delivery systems.
As is often the case with cannabis, further research will undoubtedly uncover more avenues towards novel therapeutic systems.
For more in depth information on different regulations in various countries and how this affects pharmacists, we recommend accessing our in depth modules available on our website. Here, you can find up to date information on CBMPs and how best to prescribe them. You can also explore our news section and evidence base for the latest information on this ever-changing area of research.
We urge anyone considering the use of medical cannabis products to consult with a trained medical professional prior to beginning use.