Cannabis has a potential for clinical use often obscured by unreliable and purely anecdotal reports. The most important natural
cannabinoid is the psychoactive
tetrahydrocannabinol (delta9-
THC); others include
cannabidiol (CBD) and
cannabigerol (
CBG). Not all the observed effects can be ascribed to
THC, and the other constituents may also modulate its action; for example CBD reduces anxiety induced by
THC. A standardised extract of the herb may be therefore be more beneficial in practice and clinical trial protocols have been drawn up to assess this. The mechanism of action is still not fully understood, although
cannabinoid receptors have been cloned and natural
ligands identified. Cannabis is frequently used by patients with
multiple sclerosis (MS) for
muscle spasm and
pain, and in an experimental model of MS low doses of
cannabinoids alleviated
tremor. Most of the controlled studies have been carried out with
THC rather than cannabis herb and so do not mimic the usual clincal situation. Small clinical studies have confirmed the usefulness of
THC as an
analgesic; CBD and
CBG also have
analgesic and antiinflammatory effects, indicating that there is scope for developing drugs which do not have the psychoactive properties of
THC. Patients taking the synthetic derivative
nabilone for neurogenic
pain actually preferred cannabis herb and reported that it relieved not only
pain but the associated depression and anxiety.
Cannabinoids are effective in
chemotherapy-induced
emesis and
nabilone has been licensed for this use for several years. Currently, the synthetic
cannabinoid HU211 is undergoing trials as a
protective agent after
brain trauma. Anecdotal reports of cannabis use include case studies in
migraine and
Tourette's syndrome, and as a treatment for
asthma and
glaucoma. Apart from the smoking aspect, the safety profile of cannabis is fairly good. However, adverse reactions include panic or anxiety attacks, which are worse in the elderly and in women, and less likely in children. Although
psychosis has been cited as a consequence of cannabis use, an examination of psychiatric hospital admissions found no evidence of this, however, it may exacerbate existing symptoms. The relatively slow elimination from the body of the
cannabinoids has safety implications for cognitive tasks, especially driving and operating machinery; although driving impairment with cannabis is only moderate, there is a significant interaction with alcohol. Natural materials are highly variable and multiple components need to be standardised to ensure reproducible effects. Pure natural and synthetic compounds do not have these disadvantages but may not have the overall
therapeutic effect of the herb.