The endocannabinoid system consists of the receptors CB1 and CB2 and their ligands, referred to as 2-AG and anandamide. The ligands are formed and degraded again by a number of enzymes, which are also considered to be part of the endocannabinoid system.
The two main active compounds in medical cannabis, THC and CBD, affect different receptors, and the balance between them may be important with respect to the indication one wishes to treat.
THC activates CB1 and CB2 receptors directly, while CBD has an indirect effect and can inhibit the binding of THC to the receptor. Meanwhile, the CBD can increase the level of our own endocannabinoid, anandamide. That is why the ratio between THC and CBD in medical cannabis is essential for the clinical effect.
Common to both THC, CBD and the body's own endocannabinoids is that they are fats (lipids). Thus, they are insoluble in water but readily soluble in oil. The molecules are also relatively small and can freely pass through the blood-brain barrier.
Both 2-AG and anandamide contain the fatty acid arachidonic acid. The endocannabinoids are formed and rapidly broken down in the cell, thereby regulating the activity of the endocannabinoid system.
CB1 receptors are found primarily in the central and peripheral nervous system, but also in the gastrointestinal tract. They are particularly concentrated in the part of the brain that controls cognitive functions, appetite, sleep, learning, memory, stress, pain, motor skills and nausea. When THC and CBD affect the CB1 receptors, the signalling in the brain's neurons is modulated.
CB2 receptors are found primarily in organs and cells related to the immune system, including the tonsils, the spleen, the lymph nodes and in circulating lymphocytes and neutrophils (types of white blood cells). That's why activation of the CB2 receptor inhibits the body's inflammatory response.