The definitive marijuana guide from Cannabis UK
Cannabinoids in clinical practice
by
Williamson EM, Evans FJ
ABSTRACT
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.
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