Naturally occurring cannabis (Cannabis sativa) contains a group of chemical compounds not found in other plants known as cannabinoids. Over 60 different cannabinoids have so far been identified but the role and importance of many of these has yet to be fully understood. Identified cannabinoids include Delta-9 Tetrahydrocannabinol (THC), Cannabidiol (CBD), Cannabinol (CBN), Cannabichromene (CBC) and Cannabigerol (CBG).

Of these only two cannabinoids have been well characterized - delta-9-tetrahydrocannabinol (THC) and cannabidiol (CBD).

THC is the most prominent cannabinoid since it is the principal psychoactive agent. There is an abundance of literature in the public domain on the pharmacology and toxicology of synthetic THC. By contrast, CBD is not psychoactive.

Both THC and CBD have important pharmacology: THC has analgesic, anti-spasmodic, anti-tremor, anti-inflammatory, appetite stimulant and anti-emetic properties, whilst CBD has anti-inflammatory, anti-convulsant, anti-psychotic, anti-oxidant, neuroprotective and immunomodulatory effects. CBD is not intoxicating and indeed it has been postulated that the presence of CBD in cannabis may alleviate some of the potentially unwanted side-effects of THC. There is currently limited scientific information on the pharmacology and toxicology of the other cannabinoids. Cannabinoids are believed to be effective in suppressing muscle spasticity, spasms, bladder dysfunction and pain symptoms of MS .

GW believes that the beneficial therapeutic effects of cannabis based medicines result from the interaction of different cannabinoids, hence GW's medicines consist of cannabinoids in different ratios. To date GW's research has primarily focused on the two principal cannabinoids THC and CBD. In addition GW believes that other components within the plant are also important which is why GW's medicines are made from botanical extracts.

Phytocannabinoids, Endocannabinoids and Synthetic Cannabinoids
The term "cannabinoid" has different meanings. Cannabinoids were originally defined as a group of C21 compounds uniquely produced by the cannabis plant. Subsequent development of synthetic cannabinoids and the discovery of natural cannabinoids in the body (“endocannabinoids”) has somewhat blurred this definition. The molecules derived from the plant itself are therefore now termed “phytocannabinoids”. Synthetic cannabinoids are those which have been man-made.

The Cannabinoid Receptor System
Only in the last decade or so, a natural cannabinoid receptor system has been discovered in the human body. It is by interacting with these receptors that cannabinoids exert many of their pharmacological effects. The discovery of the cannabinoid receptor system has sparked renewed interest in the therapeutic potential of cannabinoids by providing important new targets for drugs. There are at least two types of cannabinoid receptors in mammalian tissues, CB1 and CB2. CB1 receptors are present in the brain and spinal cord and in certain peripheral tissues. CB2 receptors are expressed primarily in immune tissues. There is preliminary evidence to suggest that additional cannabinoid receptor types may exist.

CB1 receptors are widely distributed but are particularly abundant in some areas of the brain including those concerned with movement and postural control, pain and sensory perception, memory, cognition, emotion, autonomic and endocrine functions. The role of the second type of receptor, CB2 receptor, is still under investigation but it is believed to mediate the immunological effects of cannabinoids.