Cannabinoids are lipophilic molecules (i.e., oil-based compounds that are not soluble in water). This means that when you place extracted hemp oils into water, they float. Cannabionoids in their natural lipophilic state do not mix with water and will not dissolve in the water. This has always been the problem for oil-based compounds—because the human body is 60% water, they have difficulty dissolving, and more importantly, absorbing these molecules.
The term “water solubility” refers to a compound’s ability to dissolve into water at a specific temperature. The term bioavailability refers to the amount of active ingredient in the compound, which makes it into the bloodstream. If an ingredient is injected directly into the bloodstream, it is 100% bioavailability.
When CBD is ingested, it is absorbed by the digestive system. From the stomach, the compounds enter the hepatic portal system, where they are carried through into the liver. The liver then metabolizes the CBD molecules, in what’s referred to as the “first pass effect.” Here, CBD can be significantly broken down before reaching the blood.
Other reasons for decreased oral bioavailability include destruction of the drug by gastric acidity, intestinal membrane enzymes, complexion with food constituents or bacterial enzymes. Foods, especially fat, can slow gastric emptying. Absorption can be limited by the short transit period of the drug through the small intestine (2-4 hours). These functions act on CBD, reducing the concentration of the compounds before passing on what remains to the bloodstream. The first pass metabolism effects a large portion of the CBD and its metabolites are excreted, which means that a lot of the benefits are literally flushed away. Lastly there are questions about liver toxicity, especially in large doses.
It is estimated that the bioavailability of CBD is as low as 5-10 percent going through the stomach into the bloodstream.