Why Bioavailability Matters for CBD

What is Bioavailability?

Bioavailability is the proportion of any compound or substance that enters the bloodstream when introduced to the body. This value varies due to many factors that affect absorption. However, the most determinant factor is the way it is administered. There are four ways in which substances can enter the bloodstream: inhalation, ingestion, absorption, and injection. This article outlines what bioavailability means for any compound, including medicines or substances found in food for example.

For instance, pharmaceuticals given intravenously have 100% bioavailability because they enter directly into the bloodstream. Substances that are taken orally have a much longer way to travel in order to enter the bloodstream. Therefore, they have a lower and variable bioavailability depending on how much the substance interacts with different acids or enzymes in the digestive system and liver (Flynn 2007).

Other methods of consumption also have variable bioavailability rates. Inhalation offers a very fast and efficient way to deliver some substances directly into the bloodstream through absorption in the lungs. However, this may have adverse and irritating effects on the lungs of some individuals (Abrams 2007). Sublingual absorption, while not as fast-acting as inhalation, enters into the bloodstream through glands under the tongue (Notcutt 2004). This can allow the substances to interact with enzymes in saliva prior to absorption or swallowing. Both of these occurrences could affect the substance’s bioavailability. Nasal sprays are another option for consumption, and allows a substance to be absorbed through the mucous membranes in the nasal passages. Transdermal patches can work to great effect for absorption directly through the skin (Lawrence 1997).

All of these methods offer a different path to the bloodstream and the absorption can vary from person to person. The specific substance in question also has an enormous effect on the bioavailability of each method. In the case of CBD, the structure of the molecule has profound implications for its own bioavailability.

Bioavailability of CBD

CBD products come in many forms. From topical ointments to edible candies, all with a fluctuating range of concentrations. For example, 10mg of CBD taken with a vaporizer is not the same as 10mg of CBD taken orally. Again, substances are much more bioavailable through the lungs than through the digestive system. For CBD consumed orally, this is partially due to the first pass metabolism effect (Pond 1984). Some of the CBD is metabolized by enzymes, mostly in the liver, but also in the digestive system before reaching the bloodstream. However, this isn’t the only factor leading to low oral bioavailability.

CBD is a lipophilic molecule, meaning that it is attracted to and dissolves in lipids, oils, and fats. This means that it does not dissolve well in water, if at all. The human digestive system is water-based but does have the ability to breakdown and absorb lipids as well. If CBD is not attached to some sort of fatty molecule, it has an extremely low absorption rate and most of it will simply pass through the digestive system without ever reaching the liver. This is the reason many oral CBD products have lipid-based absorption enhancers or are made using easily digestible fats, such as oils found in foods (Cherniakov 2017).

CBD has been studied for its bioavailability in different delivery methods. Oral bioavailability ranges from about 6-15% while vaporizing can be up to 50% (Ohlsson 1986)(Samara 1988). Topical and transdermal products have a bioavailability rate somewhere around 45%, and nasal sprays around 40% (Paudel 2010). Each product has a unique path for entering the bloodstream and therefore has different availability.

To Sum It Up

Not all CBD products and their uses deliver the same results. A 20mg transdermal patch will deliver much more CBD than a 20mg oral capsule. A CBD vaporizer will take effect almost instantly, while an ointment may release the same amount of CBD over a much longer period of time. Also, individual bodies differ in which method will work the best or be the most practical for their lifestyle. It’s important to understand the differences between CBD products and how they’re absorbed in order to find the right product for you.