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Clearing the smoke over medical use of cannabis

Cannabis

This item first appeared in 2007

Thames and Kennet Regional Group looks into the controversial substance, but does not inhale

Cannabis has been used as a medicine for thousands of years and scientists are now able to support some of the traditional uses with modern scientific techniques. The use of cannabis as a medicine was discussed by Liz Williamson, professor of pharmacy at the University of Reading, UK, at a meeting of the Thames and Kennet Regional Group on 21 February 2007 at the university’s chemistry department.

The medicinal properties of the plant were first reported in around 2000BC in the ancient Arthava Veda, a Sanskrit text, where it was advocated for treating pain and inflammation, in rheumatism, menstrual and other pain and as a sedative, anaesthetic, appetite stimulant and hypnotic. In 1840 an Irish surgeon, William O’Shaughnessy, who had been working in India, introduced it to the West for medicinal use.

Cannabis contains a number of active ingredients, the most important of which are the cannabinoids, such as tetrahydrocannabinol (THC), which is responsible for the psychoactivity. There are other cannabinoids, which also have biological effects, as well as an essential oil and flavonoids. THC acts at CB1 receptors (which are responsible for psychoactive effects and muscle relaxant effects of cannabis) and these are found in neurons, especially in the central nervous system, and also CB2 receptors, which are less well known, but are responsible for immune and anti-inflammatory effects. The body itself contains natural cannabis-like compounds, called ‘endocannabinoids’ and it is these which the plant constituents mimic.

Research on cannabis and cannabinoids increases every year and has already provided a wealth of knowledge, but there remains much to learn regarding the actions of the other plant constituents. Many of the known actions of the plant have become apparent as a result of either smoking or ingesting the whole plant extract and not isolated THC (tetrahydrocannabinol), so Williamson and her team have tried, in several systems ranging from neurological models of status epilepticus and muscle spasticity to cell culture models of proliferation and release of inflammatory cytokines, to compare the activity of a total extract of the herb with matched concentrations of isolated THC. In most of these cases its was found that the activity of the herb is better than that of isolated THC.

Paradoxical effects of cannabis extracts have been observed, and in some cases removal of the THC from the extract even enhanced the activity. Williamson has found that cannabis can enhance the growth and differentiation of stem cells into bone cells (osteoblasts) and can reduce the turnover of skin cells and inflammation, which may help with skin conditions such as psoriasis. At present the studies are only in vitro, and have not yet been taken into the clinic, but the work is relevant not only to the possible therapeutic use of the drug, but also because it is taken illicitly so widely.

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