Bioavailability of CBD. What does it mean and why is it important?

25. 01. 2024

CBDs offer great potential for your health or treatment. For its high safety and non-addictiveness, it is a very attractivealternative to a number of conventional drugs.

For the best effectiveness, CBD must easily enter the endocannabinoid system in the first place. This means that it has to be absorbed by the bloodstream, which is a mechanism known as bioavailability. Moreover, CBD has to remain long enough within the bloodstream so that it can be distributed to the tissues and organs where it is needed.

How much of the dose does actually get absorbed?

This depends on a process known as pharmacokinetics. Simply put, pharmacokinetics refers to the sum of ongoing mechanisms of absorption and elimination happening within the body, characteristics of the used CBD, and multiple external factors. All of which can help or restrain how well CBD is assimilated and used by the body.

Furthermore, the way how CBD is administrated directly affects the amount and distribution into the bloodstream.



 

In this article, we are going to look at various ways that are used for administration of CBD, namely peroral, inhalational, mucosal, transdermal, and intravenous. We are going to discuss details regarding these methods, including their pros and cons, which are presented by contemporary scientific findings. Last but not least, we are going to look into the important factors that affect the absorption and metabolism of CBD. You will learn how to make the best of these factors so that you can choose the ideal way of administration depending on what you wish to get out of it.

Oral administration: Capsules, oils, and foods

Oral CBD supplements, such as drops, capsules, tincture, foods, and drinks fall into the most favourite way of consumption. However, oral administration has the lowest bioavailability of all methods named above in the introduction, which ranges from 6 to 19 percent. One of the reasons is that CBD does not get absorbed quickly enough as most of it gets excreted by the body. This is caused by the fact that CBD is fat-soluble, which makes it difficult to be absorbed.

Further, digestive acids and enzymes destroy a large amount of CBD before it gets a chance to be effectively used. Plus, a small amount, which makes its way through the intestinal wall, is metabolised by the liver before it is supplied into the body. There has been recorded the half-life of oral CBD (it is a time required for a quantity of CBD to be reduced to half of its initial amount by leaving the bloodstream) between 10 to 17 hours at as high doses as 750 – 1500 mg. It can be noticeably shorter compared to other methods of administration.

With oral administration, peak levels tend to be noticeably lower compared to other methods. 

There has been an experiment showing the findingsthat biscuits filled with 40 mg of CBD resulted in the bloodpeak levels between 1.5 and 3 hours after ingestion.

On the other hand, the longer duration of the active effect compensates the low absorption. That is considered as a good advantage. A study done on lab animals has discovered that perorally consumed molecule of CBD stays in the body for up to 4.2 hours. While, as for CBD administrated by injection,that was performed for the same study, the time was 3.3 hours. Finally, it has also been found out that orally administrated CBD in animals leads to its higher level in the brain compared to inhalation methods.

Inhalation of CBD: vaping and smoking

Inhalation is an effective way of consumption because it bypasses the digestive system, including the liver. It allows CBD to be easily absorbed by the thin membranes that line the lung sacks, where it passes directly into the bloodstream. There are several ways to inhale CBD.

1. Smoking

The most basic inhalation method is smoking. In this case, the smoked material consists of unprocessed hemp buds rich in CBD (unlike hemp,that is high in THC). Smoking has a bioavailability of 31% and a single dose, containing about 19 mg of CBD, can rise to thepeaklevel in the bloodstream within 3 minutes. The half-time of smoked CBD is about 31 hours.

The downside of smoking is that it creates by-products of burning processes, which can irritate and, in some cases, damage the lungs. These include fluorene, pyrene, acrylonitrile, and acrylamide.

2. Vaping

A more sophisticated and less irritating inhalation method that is similar to smoking is vaping – using a vaporizer or vaporization pen.

With this method, you can use carefully chosen liquid CBD oil stored in a cartridge or hemp rich in CBD. You inhale the steam which is formed by the heating unit.

Vaping produces concentrations of CBD in the bloodstream comparable to smoking. As for pharmacokinetics, it also shows similar results. With vaping, there is a certain risk of lung irritation, although less than with smoking.

3. Aerosol inhalers

As its name already reveals, the aerosol inhaling spray (or simply just ‘inhaler’) is a device that releases CBD in the form of aerosol to be inhaled into the lungs. Inhalers are usually used in hospitals to administrate the drug through damaged or sensitive lungs.

They come to theblood peaklevel in approximately 36 minutes.



 

Sublingual CBD: Drops and Sprays

This method uses the ability ofCBD to be absorbed directly through the mucous membranes of the mouth and nose, bypassing the digestive system, and leading directly into the bloodstream.

1. Sublingual drops

It has been measured that theblood peak levels, which involved administering liquid CBD drops under the tongue, were approximately 2 hours.

A simple way how to improve the absorption of sublingual CBD is to hold it under the tongue for 20 to 30 seconds before swallowing. This allows the mucous membranes more time to absorb CBD before it enters the digestive tract.

2. Oral spray

Another study has shown that oral spray composed of a balanced combination of THC and CBD (50 % each) reached theblood peak levels in 3.6 hours for a 5mg dose and 4.5 hours for a 15 mg dose of CBD. That said, the peak blood levels of a three-times higher dose offered about 20 % of additional time.

Likewise the previous example, holding the dose under the tongue before it is swallowed optimises the administration the same way – it allows more time for absorption. 

3. Nasal spray

The absorption through the thin nasal mucous membranes is quite rapid, and it brings maximum concentrations in the blood in just 10 minutes or less.

Transdermal CBD: Transdermal patches and external administration

CBD can enter the bloodstream through an adhesive patch placed on the skin, which is a method known as transdermal administration. However, highly fat-soluble cannabinoids are repelled by the layer of skin, acting as an absorption barrier.

A practical solution for this is to combine CBD with ethanol, which makes it more water-soluble. It has been confirmed that this trick increases the absorption four-times.

Transdermal CBD is useful for maintaining steady levels to avoid fluctuation. Although it enters the bloodstream relatively slowly compared to other methods, it can be an advantage to prevent potential side-effects that usually are associated with blood peak levels being reached too quickly.

Transdermal administration is especially useful in chronic inflammatory conditions or relieving discomfort in patients with chronic pain who have not responded well to conventional treatment.

This method is also more convenient than any other, increasing the likelihood that patients with such conditions will reach for it.

Intravenous CBD: Injectable CBD (for hospital use only)

Intravenous administration that is applied directly into the bloodstream offers 100% bioavailability. However, the blood level decreases rapidly. Hence, it may not be the most effective way of taking CBD. A study done on marijuana smokers has shown that 20 mg of intravenous CBD had four-times higher bioavailability than a 19 mg dose that was smoked. However, within the first hour, these values dropped by about 93%. In other words, the half-life of intravenous CBD (24 hours) was lower than the half-life of the smoked form (31 hours).

Factors that affect the absorption and elimination of CBD

The pharmacokinetics of CBD are subject to many internal and external factors. Some of them can be controlled by the user in order to make an advantage out of them. For those that are out of the control, the efficiency can be maximised by the most suitable administration regarding the specific health condition.

Here are a few out of many variable parts of CBD pharmacokinetics:

1. Medical condition

A medical condition can affect the absorption of CBD in certain ways. It is, therefore, necessary to adjust the dosing or the way of administration.

Liver function

The liver has an essential function in removing CBD in the way of preparing it for exertion from the body. If the liver shows impaired function, it notably affects the CBD efficiency and how long it stays in the body.

In another study, after taking the same dose of 200 mg of CBD, participants with moderate to severe hepatic impairment had higher concentrations of CBD in the blood compared to healthy subjects. It also took longer to clean it out of the system. 

This means that more CBD gets into the circulation where it also stays longer. As a result, these individuals experience stronger effects than users with healthy liver.

Other health effects

The bioavailability of CBD can also be affected by neurological health problems.

Patients with Huntington's disease, who have been given peroral supplements containing 700 mg of CBD for six weeks, showed low peak levels ofabsorption, without any beneficial effects.

On the other hand, healthy volunteers, who have been given 600 mg of peroral CBD, showed better absorption and higher blood levels.

2. Dosing

It is possible to shift the equation in favour of better absorption by using higher doses. For example, an increase of peroral spray from 5 mg to 10 mg can double the absorption. It also has been found out that if you increase the dose from 10 mg to 20 mg, this results in three-times higher absorption.

However, when the user goes for even higher doses, between 400 mg and 800 mg, it seems that they reach the threshold as they no longer lead to higher absorption rates. 

This partly happens because the tissues are already saturated and therefore unable to absorb more CBD.

3. Fasting vs saturation

The absorption of CBD is much better – three to five times – when you use it with food compared to the administration on an empty stomach.

Since CBD is fat-soluble, fats from healthy sources such as avocados, fish high in omega-3 fatty acids, nuts, and seeds are good helpers. CBD dissolves and break down into smaller parts that are easier to absorb.

Food also helps to slow down the cleaning processes that are responsible for removing CBD from the body. An administration on an empty stomach had a cleaning time up to ninetimes shorter compared to post-meal or with-meal administration. 

The presence or absence of food can have a larger effect on the cleaning processes than dose levels. In an experiment, when single doses of peroral sprays at the levels of 5 and 20 mg have been measured, it was found out that the higher dose was cleaned out of the system just by 14 % faster.

4. Heat treatment

Heating of hemp extracts (which occurs in some lower-quality processing methods) converts cannabinoids into forms that are also active but get to be absorbed less effectively. A study has found that maximum CBD levels were four times higher in cold processed extracts compared to heat-treated extracts.

5. Supplements with piperine

Piperine, which is, for example, found in black pepper, functions on several levels, and provides strong absorption-enhancing effects.

It stimulates the transport of molecules in the intestinal lining, which are responsible for transferring CBD through the intestinal membrane and into the bloodstream. Once CBD is absorbed, piperine inhibits enzymes that degrade CBD, giving it more time to reach its target tissue where it gets absorbed and utilised.

As for oral CBD supplements that are made with piperine, there has been recorded a sixfold higher increase in the maximum concentration in the bloodstream compared to the same piperine-free CBD supplement. That is quite impressive!



 

Summary

CBD is widely available nowadays. However, as for how CBD gets processed within the human body, science still finds itself in the early stages. In addition, there are vast differences in the rate of absorption and assimilation of CBD in different kinds of animal species, including humans. Thus, for example, some tests, performed on lab animals such as mice, canshow different results on humans.

Hence it follows, we can draw several conclusions based on these findings:

Oral CBD – It has the lowest bioavailability, but this can be compensated by using supplements such as piperine, or you can use it along with fats.

Inhalation of CBD – This method offers a high rate of absorption. However, it can lead to lung damage over time.

Transdermal CBD – It offers slow and stable administration, which is highly beneficial for patients who need to maintain a consistent level of CBD in the bloodstream.

Sublingual CBD – Oral sprays and sublingual drops are comparable to oral CBD when it comes to absorption rates. At the same time, nasal inhalators offer a quicker absorption rate comparable to inhaled CBD without negative effectson the lung tissue.

Intravenous CBD (IV) – It is the most effective way of administration. The flip side of this method is that CBD administrated this way rapidly leaves the body. This method is reserved only for healthcare professionals.

Finally, it is important to bear in mind that the user's health has an effect on which forms of administration may or may not work. In case of uncertainty, always consult the best options with medical professionals who will provide you with answers based on your current health condition.