Following cloning of the endogenous receptor for THC, namely the CB1R, endogenous CB1R ligands, or “endocannabinoids” (eCBs) were discovered, namely anandamide (AEA) and 2-arachidonoylglycerol (reviewed in ). The CB1R is an inhibitory Gi/o protein-coupled receptor that is mainly localized to nerve terminals, and is expressed on both γ-aminobutryic acid-ergic and glutamatergic neurons. eCBs are fatty acid derivatives that are synthesized on demand in response to neuronal depolarization and Ca2+ influx, via cleavage of membrane phospholipids. The primary mechanism by which eCBs regulate synaptic function is retrograde signaling, wherein eCBs produced by depolarization of the postsynaptic neuron activate presynaptic CB1Rs, leading to inhibition of neurotransmitter release . The “eCB system” includes AEA and 2-arachidonoylglycerol; their respective degradative enzymes fatty acid amide hydroxylase (FAAH) and monoacylglycerol lipase; the CB1R and related CB2 receptor (the latter expressed mainly in the periphery); as well as several other receptors activated by eCBs, including the TRPV1 receptor, peroxisome proliferator-activated receptor-γ, and G protein-coupled 55 receptor, which functionally interact with CB1R signaling (reviewed in [21, 24]). Interactions with the TRPV1 receptor, in particular, appear to be critical in regulating the extent to which eCB release leads to inhibition or facilitation of presynaptic neurotransmitter release . The TRPV1 receptor is a postsynaptic cation channel that underlies sensation of noxious heat in the periphery, with capsacin (hot chili) as an exogenous ligand. TRPV1 receptors are also expressed in the brain, including the amygdala, periaqueductal grey, hippocampus, and other areas [26, 27].
Daniel Clauw, MD, professor of anesthesiology at the University of Michigan, believes that CBD may have real benefits for people living with chronic pain. He cites a recent clinical trial from pharmaceutical company Zynerba (for which Dr. Clauw has consulted) that found that a CBD-derived topical drug provided pain relief to patients suffering from knee osteoarthritis.
In the United States, non-FDA approved CBD products are classified as Schedule I drugs under the Controlled Substances Act. This means that production, distribution, and possession of non-FDA approved CBD products is illegal under federal law. In addition, in 2016 the Drug Enforcement Administration added "marijuana extracts" to the list of Schedule I drugs, which it defined as "an extract containing one or more cannabinoids that has been derived from any plant of the genus Cannabis, other than the separated resin (whether crude or purified) obtained from the plant." Previously, CBD had simply been considered "marijuana", which is a Schedule I drug.