The therapeutic effect of each preparation is conditioned by its absorption (intestinal or pulmonary) and by the specific metabolites produced within the human body. Important is the difference between oral and inhalation preparations. In fact, inhaled cannabinoids and terpenes arrive via the lungs directly into the blood stream, whereas the absorption of ingested compounds is significantly conditioned by the condition of the intestine and liver. These factors, which affect the absorption and metabolism of cannabis, may result in different effects on the body, even when using the same type of cannabis. The route of administration and doses to be used are decided by the doctor; taking into account the patient’s therapeutic needs and the pharmacokinetic properties will be consequential. Following oral intake of cannabis or synthetic THC (e.g. dronabinol), only 10-20% of THC enters the circulatory system due to extensive hepatic metabolism and limited solubility of THC in water (Grotenhermen, 2003; Huestis 2007). After oral administration, it takes between 30 and 90 minutes for the pharmacological effect to begin, the maximum effect being obtained within 2-4 hours after intake.
Plasma concentrations of THC depend on the dose taken. For example, after oral administration of 20 milligrams of THC, maximum plasma concentrations of between 4 to 11 nanograms per milliliter are reached between one and six hours after oral intake. CBD shows bioavailability and oral absorption similar with THC. After oral intake of 10 milligrams of CBD the peak concentrations are 2.5 ± 2.2 nanograms per milliliter.
Following inhalation of cannabis, the bioavailability of THC varies from 10 to 35%, the pharmacological effect starts after a few minutes and peaks approximately one hour after inhalation and sees a decline in 3-4 hours (Grotenhermen 2003). Maximum plasma concentrations of THC occur within ten minutes after the first inhalation. The number, duration and interval of aspirations influence the maximum plasma concentrations and the time to peak (Grotenhermen 2003, Huestis 2007). In the case of inhalation intake, as well as in oral intake, plasma THC concentrations vary depending on the inhaled dose. For example, following inhalation intake of 16 or 34 milligrams of THC, plasma concentrations reached within the first ten minutes vary respectively ranging from 50-130 and 70-270 ng THC per milliliter of plasma after administration and falling below 5 ng/ml two hours after the last inhalation (Huestis 2007).
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