Most cannabis consumers are likely perusing the wide variety of cannabis products out there without a thought to bioavailability. However, not all methods of ingesting cannabinoids are created equal, in terms of how effectively they are delivered to the body.
This article explores what bioavailability is, how it is influenced, and how the active compounds in cannabis vary in their bioavailability among the common consumption methods. Additionally, answering the questions about why bioavailability is an important concept to consider when choosing the right cannabis product for each person’s needs.
What Is Bioavailability?
Bioavailability refers to the proportion (or percentage) of an active drug that enters systemic circulation unaltered after being introduced into the body. By this definition, if a cannabinoid like tetrahydrocannabinol (THC) is introduced by the intravenous route, it is 100% bioavailable because all of the compound will reach the systemic blood supply.
On the other hand, when eating a dose of a cannabis edible with 30 mg of THC and only 1.8 mg is absorbed and used by the body unaltered, then the bioavailability is just 6%. Bioavailability is therefore a metric of how well a substance works in the body.
Influencing Factors
Generally speaking, the higher the bioavailability, the more the drug is losslessly being put to work in the body towards its intended effects. As discussed below, the delivery method plays a crucial role in a drug’s bioavailability. In comparison to the IV route, other administration routes show much lower bioavailability due to some influencing physiological factors.
Oral bioavailability is lower because of an effect known as first-pass metabolism. When a drug is taken orally, it is first absorbed by the digestive system and then makes its way to the liver via the portal vein. The liver then metabolizes the drug before it reaches the systemic blood supply.
This effect greatly reduces the amount of the drug that reaches its target destination (usually the brain), therefore lowering the bioavailability. Although the first-pass effect is mostly associated with the liver, it can happen in other metabolically active tissues in the body (including the lungs, vasculature and gastrointestinal tract) to varying extents depending on the person.
Another important influencing factor to consider is the drug or substance itself. Cannabinoids are hydrophobic compounds, meaning they do not readily dissolve in water. Since the body is mostly water, this structure is not conducive to high availability in the body itself.
For this reason, cannabidiol (CBD) and THC’s oral bioavailability can be improved if it is consumed alongside a snack high in fats. Indeed, animal studies where THC and CBD were consumed in conjunction with lipids showed two and a half times and threefold increases in bioavailability, respectively. In essence, the fats helped to solubilize the cannabinoids, which helps them diffuse and absorb into the bloodstream more readily.
Cannabis Bioavailability by Consumption Method
There are dozens of ways to consume cannabis with a wide variety of products on the market. Accordingly, it can be tricky to know what product to choose that best suits each person’s needs without an understanding of bioavailability. As discussed, the route of administration makes an enormous difference in how cannabinoids are absorbed and put to use by the body. Here’s a look at the bioavailability of THC via the most common consumption methods.
Inhalation
Apart from being the most common (with vapes, joints, bongs, etc.), the inhalation route is a rapid and efficient method of delivering cannabis from the lungs to the brain. Vaporizing cannabis is a preferred method of inhalation because it isn’t associated with the same damaging effects to the lungs, since cannabis vapor contains fewer carcinogens and toxins.
The bioavailability of THC is hugely variable when inhaled, varying from 2-56%, with an average of around 30%. The variability arises in part from differences in the product, smoking device and how it is smoked. This includes how long each hit is held, the number and spacing of puffs, the inhalation volume, and more. Generally, vaporizing cannabis is the most bioavailable inhalation method, consistently showing levels greater than 50%.
Sublingual
Sublingual administration involves a handful of products such as tinctures, sprays, tablets and strips. The sublingual method involves placing the liquid or strip under the tongue for a minute or two, where it’s absorbed through the mucus membranes into the bloodstream. This method of administration avoids first-pass metabolism by the liver and therefore shows an improved bioavailability. For THC, the bioavailability roughly ranges from 4-20%. For CBD, this is one of the most common consumption methods and shows bioavailability of up to 20%.
Oral
Oral cannabis products include edibles (foods, candies, baked goods), syrups, capsules beverages. This method of delivery shows the lowest bioavailability of all due to the fact that the cannabinoids are metabolized heavily by the liver before entering the bloodstream. The bioavailability of THC via the oral route ranges from 4-12%, with absorption highly variable.
Compared to the inhalation route, this method also involves a much slower absorption rate since it takes time for the cannabinoids to move through the digestive system and into the systemic circulation. For this reason, edibles may take 30-60 minutes to kick in and can last over six hours, making it an ideal method if the desire is to slowly absorb small quantities of cannabinoids throughout the day.
Topical & Transdermal
Topical and transdermal cannabis products are commonly used to treat local pain and inflammation. Many topical products exist on the market, including lotions, butters, creams, balms, sprays, soaps and oils.
On the other hand, transdermal patches are unique. They contain cannabinoids alongside carrier agents that help the active ingredients steadily and efficiently pass through the skin barrier and into the bloodstream. The average CBD and THC bioavailability via these routes are unknown due to a lack of human studies. But according to one study, CBD has been shown to have tenfold higher permeability across skin tissues when absorbed transdermally compared to THC.
Generally, bioavailability is improved in this route due to the fact that topical and transdermal applications avoid the first-pass metabolism. However, since cannabinoids are highly hydrophobic, the movement of these fat-soluble compounds through the aqueous layer of the skin is a limiting step that lowers the rate of absorption.
Why Is Bioavailability Important?
Without an understanding of how much of an administered dose is actually being put to work in the body, it can be difficult to tailor dosages that maximize therapeutic benefits and minimize unwanted side effects. In the realm of medicinal cannabis, knowledge of bioavailability allows patients to better titrate an optimally effective dose that’s personalized to the metabolic quirks of their body and to the condition they are treating.
Indeed, the higher the bioavailability, the less the dose required to experience a given level of effects. Individuals with severe or chronic pain, for instance, may benefit from high bioavailability forms of consumption like vaporization, where the cannabinoids can work quickly and potently without first-pass degradation by the liver or gut wall.
Disclaimer: Cannabis is potentially categorized as an illegal drug. Reality Sandwich is not encouraging the use of these drugs where prohibited. However, we believe that providing information is imperative for the safety of those who choose to explore these substances. This guide is intended to give educational content and should in no way be viewed as medical recommendations.
