Cannabinoids are delivered to the bloodstream through the lungs (when inhaled), the digestive system (when consumed), or the skin (when applied topically). Once in the bloodstream, they are available to the brain and central nervous system.

Inhalation is the fastest method, with peak blood levels achieved within 5-20 minutes. Oral ingestion is slower because cannabinoids go through the gastrointestinal tract before entering the blood stream. The bioavailability of cannabinoids in the body is an important area of ongoing research with implications for the medicinal use of cannabis.

There are two major types of cannabinoid receptors in our bodies, CB1 and CB2. The CB1 receptors are found in the central nervous system, on brain cells and in the peripheral nervous system. The CB2 receptors are generally found on immune cells. Humans have many thousands of receptors that we still have not identified or fully understood. A common characteristic is that receptors bind with naturally-occurring substances such as hormones (e.g., estrogen, testosterone) and growth factors (e.g., insulin) as well as with exogenous substances introduced into the body to mimic the effect of endogenous substances.

Having discovered cannabinoid receptors, scientists began to search for the naturally-occurring ligand that binds with the receptors to achieve a biologic purpose. Their research uncovered two endocannabinoids and 2—AG. Both are agonists that influence pain, appetite, motor learning, and synaptic plasticity.

Modern cultivation methods enable production of strains with consistent ratios of terpenes to cannabinoids.

Typical plasma levels of THC after smoking cannabis are 70-160 nanograms per milliliter (ng/ml). Because THC is lipid soluble, it rapidly leaves the bloodstream and goes into the fatty tissues of the body. When cannabis is smoked or inhaled, only about 10-25% of THC is absorbed into the bloodstream from the lungs and about 1% of that reaches the brain rapidly.

This is important because brain cells possess unique binding sites for cannabinoids called cannabinoid receptors. When cannabinoids bind to these receptors, they trigger the pharmacological effects such as pain mitigation, nausea suppression, and appetite stimulation. After the patient stops ingesting cannabis, plasma levels of THC typically decrease to less than 20 ng/ml within 30-45 minutes. Pharmacological activity peaks at about 20 minutes after inhalation and is gone within 3 hours.

When ingested orally, the pharmacological effects of THC are delayed by 30-90 minutes, peak after 2-3 hours and last for 4-12 hours. Bioavailability by ingestion is affected by liver metabolism and varies greatly (4-12%), making oral treatments difficult to manage.