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The preferred forms of ingestion of cannabis preparations for medicinal use are inhalation (smoking cannabis flowers, vaporisation via vaporizer) and oral ingestion (cannabis-based medicines such as dronabinol/THC, Sativex, nabilone and CBD extracts). Less common are rectal use via homemade suppositories and external use on the skin.
Depending on the application, the absorption of THC into the blood, the distribution of THC in the body, the duration until the onset of the effect, the time of maximum effect, the duration of effect of THC, the degradation as well as the excretion of THC differ. This article compares inhalation with oral intake.
1. how much THC reaches the bloodstream after smoking or eating cannabis products?
2. How is THC distributed in the body and how much THC reaches the brain?
3. how much THC passes through the placenta to the fetus and how much enters the breast milk of nursing mothers?
4. what is the concentration of THC in the blood?
5. how is THC broken down in the body and how long are these breakdown products detectable?
6. how is THC and its degradation products excreted in the stool and urine?
7. how do the effects of THC progress in relation to the course of the concentration in the blood?
These questions arise for every pharmacologically active substance, for every poison, for every drug and every important food component. They are described by the so-called pharmacokinetics of a substance, by the movement of the substance through the body, by its absorption, distribution, metabolism and excretion.
How much THC reaches the bloodstream?
As with many other substances, the pharmacokinetics of THC also differ depending on the type of absorption. In the case of THC, these are essentially inhalation (smoking, vaporisation) and oral absorption (eating, drinking). Absorption via the skin, the oral mucosa, the conjunctiva of the eyes and the rectum (suppositories) do not play a relevant role in the use of cannabis in the recreational sector, but may be of interest in the medical sector.
When smoking, THC is detectable in the blood within a few seconds after the first puff with maximum blood concentrations about five minutes after starting to smoke. About 10 to 35 percent of the THC in a cannabis cigarette reaches the bloodstream. Habitual users achieved a better yield on average than inexperienced cannabis smokers in studies. This yield is influenced by the depth of inhalation, the duration of the drag and the length of time the air is held. Losses occur due to the destruction of part of the THC by combustion, side currents and incomplete absorption of THC by the mucous membrane of the respiratory tract. About 30 percent is lost through combustion, and in a test with a vaporizer it was found that on average about 35 percent of the inhaled THC was immediately exhaled again.
In the case of oral intake (eating, drinking), absorption is slow and uncertain. Maximum THC blood concentrations are generally found after 60 to 120 minutes. Part of the THC is broken down by gastric acid, but most is absorbed in the upper gastrointestinal tract and reaches the liver via the portal vein. In the liver, most of the THC is broken down immediately, so that only 4 to 12 percent of the THC enters the entire bloodstream. However, some of the degradation products of THC have a similar effect to THC and contribute to the overall effect. This is especially true for the degradation product 11-hydroxy-THC (11-OH-THC).
How much THC reaches the brain and other organs?
About 90 percent of the THC is found in the watery part of the blood after absorption, in the so-called blood serum. THC is predominantly bound to proteins there and thus flows through the blood vessels. There is only little "free THC" in the blood because THC is not very soluble in water.
Because of this poor water solubility but good fat solubility, the relationship between the THC concentration in the blood and the THC concentration in other body tissues, especially fat-rich tissues, changes relatively quickly. THC penetrates relatively quickly into tissues with good blood supply, including the liver, heart, lungs, muscles, spleen, kidneys and placenta.
Only about one percent of THC given intravenously, i.e. fully absorbed, is in the brain at the time of maximum mental effects. This relatively low concentration in the brain is probably due to the strong blood flow to the brain, which brings THC into the brain relatively quickly, but also out again quickly. It seems that the THC degradation product 11-hydroxy-THC enters the brain faster and achieves higher concentrations than THC itself. Since 11-hydroxy-THC is also psychoactive and is formed in the liver to a greater extent during oral intake (eating, drinking) than during inhalation, it can be assumed that this degradation product contributes significantly to THC effects, especially during oral intake.
Subsequently, THC and its degradation products accumulate in less well perfused tissues and finally in body fat. The exact composition of the material that accumulates in fat is unknown. Among them are unchanged THC and its degradation products, partly in chemical compounds with fatty acids.