There are three main routes of administration of CBD oil: oral, sublingual and topical.
Cannabidiol (CBD) oil is a formulation made up of cannabis extracts and food or pharmaceutical type oils. Cannabis extracts are obtained by extracting (there are different extraction technologies, solvent, CO2, etc.) of flowers or / or leaves and / or the whole plant. It is therefore not a native oil but composed so that it is consumed more easily. CBD oil is frequently sought after by those looking to reap the benefits of the plant without having the psychoactive effects of its cousin, THC, the main active ingredient in cannabis.
The body absorbs CBD in different ways, and the method of consumption you choose will determine its effectiveness. Understanding the relationship between the route of administration of CBD and its absorption into the body is therefore crucial in choosing the most suitable method of administration for your needs.
A little scientific terminology
Good health is ensured through the homeostasis of our physiological system, directly thanks to a special system called the “endocannabinoid system”. In order for CBD to become active in the body, after entering, it must reach these cannabinoid receptors that make up our endocannabinoid system . This process is scientifically determined as absorption.
The total amount of CBD absorbed by the body is called bioavailability. Besides the concentration and amount of substance absorbed, bioavailability determines how much substance will be available in your system to provide the expected results. For example, a bioavailability of 15% means that 15% of the CBD consumed has become active in the body, while the remaining 85% has been eliminated as waste, unused by the body.
The path CBD takes when it enters your body, the processes it participates in, and the changes it undergoes are known as pharmacokinetics. The pharmacokinetics of CBD differ slightly from person to person. This varies in particular depending on the route of administration – whether the CBD oil is ingested, located under the tongue or applied topically. 
What are the different ways of administering CBD oil?
How CBD oil is consumed or applied to the body is defined as the route of administration. It is extremely important in determining the absorption and distribution of the substance in order to obtain the desired effects.
There are three main routes of administration of CBD oil: Oral, sublingual and topical. If we omit to talk about vaping – one of the methods of consumption that you have no doubt heard of – it is because it is strongly advised not to smoke CBD oil. Burning CBD oil, especially when diluted in polyethylene or propylene glycol (PEG), indeed generates carcinogenic compounds.
“It’s very dangerous, because if you heat oil and inhale it, you can have some kind of pulmonary inflammatory reaction, which can lead to death. “says Dr. Martin Juneau, cardiologist at the Montreal Heart Institute, in an article published by Radio-Canada just a few months ago.
Also, the pulmonary bronchi can become blocked with lipid droplets if you inhale large amounts of CBD oil.
Let’s focus on the safest methods:
Oral route of administration
You can take CBD oil orally, mixing it with liquid or food, which helps reduce the intensity of the taste.
When you take oral CBD oil, your digestive system first processes the compound. It enters the stomach and eventually ends up in the liver. The liver breaks down some of the CBD molecules and delivers the rest to the bloodstream. This form of administration is exactly how vitamins and other daily supplements are taken most often.
Ingestion, while considered by most to be the easiest method of administration, is not the most effective at absorbing high levels of CBD. This process is not fast – it takes up to 2 hours for some people – and during this process some of the CBD is lost in the liver and the digestive tract (this is called first pass metabolism. ) .
As a result, you will have to wait longer for CBD to take effect. The latter may also not be as effective (as so much was lost during the ingestion process).
Sublingual route of administration
The oral mucosa is well vascularized and relatively permeable allowing systemic absorption of CBD, while somewhat avoiding first-pass metabolism. In general, when CBD oil is administered sublingually, its bioavailability is excellent. But on one condition, it must be held under the tongue for about 1 minute so that the mucous membranes of the mouth can absorb the active ingredients of the oil. During this time, pass the oil vigorously around your mouth and even between your teeth; this will cause the CBD to reach more capillaries. In this case, the membranes in our mouth can transfer this compound directly into the bloodstream, completely bypassing the digestive system and hepatic metabolism. 
The effects of CBD oil are usually noticeable for up to 30 minutes after sublingual administration, with peaks in blood levels reported between 1 and 5 hours. This form of CBD is best taken for long-term supplementation. To maximize the effectiveness of CBD oil, specialists recommend consuming it on a full stomach. CBD is fat soluble, so consuming a healthy dose of fat with your daily servings can increase the bioavailability of the oil you swallow five-fold.
Dermal route of administration
When CBD oil is applied topically or directly to the skin, it never enters the bloodstream but can be absorbed through the skin surface to interact with nearby cannabinoid receptors. It affects receptors specifically expressed in the skin, such as localized CB-CB-2 cannabinoid receptors, and provides localized improvements in the skin. After all, our skin is built to act as a barrier that protects our internal organs from the outside world!
However, there is a way around this protection. You should apply CBD topicals liberally and vigorously to the target area, to ensure that the CBD is actually absorbed.
Topical applications of CBD oil appear to provide an excellent response to localized problems; skin problems, muscle pain, osteoarthritis and arthritis etc… For long term health benefits or as a dietary supplement people will probably choose oral or sublingual consumption.
 – Endocannabinoid System Acts as a Regulator of Immune Homeostasis in the Gut – PubMed https://pubmed.ncbi.nlm.nih.gov
 – Marilyn A. Huestis (2007). Human cannabinoid pharmacokinetics. Chem.Biodivers. 4: 1770-1804.
 – István Ujváry and Lumír Hanuš, Human Metabolites of Cannabidiol: A Review on Their Formation, Biological Activity, and Relevance in Therapy. Cannabis and Cannabinoid ResearchVol. 1, No. 1
 – Narang, N., & Sharma A, J. (2011). Sublingual mucosa as a route for systemic drug delivery. International Journal of Pharmacy and Pharmaceutical Sciences, 3(Suppl 2), 15–22 ijppsjournal.com/Vol3Suppl2/1092.pdf