Research exploring new ways of exploiting the full medicinal uses of cannabis while avoiding unwanted side-effects will be presented to pharmacologists Tuesday, 15 July by leading scientists attending the Federation of European Pharmacological Societies Congress, EPHAR 2008.
Cannabis is a source of compounds known as cannabinoids, one of which, THC - the main chemical responsible for the 'high' - has long been licensed as a medicine for suppressing nausea produced by chemotherapy and for stimulating appetite, for instance, in AIDS patients.
More recently, the cannabis-based medicine Sativex was licensed both for the symptomatic relief of neuropathic pain in adults with multiple sclerosis and as an adjunctive analgesic treatment for adult patients with advanced cancer. Sativex contains approximately equal amounts of THC and the non-psychoactive plant cannabinoid, cannabidiol.
"THC works by targeting molecules in our bodies called cannabinoid receptors" said Roger Pertwee, Professor of Neuropharmacology at the University of Aberdeen, who is co-chairing the cannabis symposium.
"So some current research is focused on designing drugs that only target cannabinoid receptors in the part of the body relevant to the disease in question and not the receptors in the central nervous system involved in the unwanted effects of cannabis."
A further approach to avoiding the psychoactivity caused by THC involves harnessing the body's own cannabis, called 'endocannabinoids'.
"We don't have cannabinoid receptors just in case we come into contact with plant-derived chemicals that activate them but rather because we have our own molecules that do this," said Christopher Fowler, Professor of Pharmacology at Umea University, in Sweden, and co-chair of the meeting.
"The neat thing about endocannabinoids is that they are often produced only when we need them, such as when our bodies are damaged in some way; pain, for example, leads to a release of endocannabinoids in a region of the brain that is involved with pain control.
"The problem with this natural protective 'endocannabinoid system' is that it is too short-lived to be of great benefit - enzymes in our bodies quickly breakdown or metabolise the endocannabinoids negating their effect. It's a bit like a bathtub without a plug - the water is turned on but rapidly disappears down the plughole. This suggests an immediate target: block the plughole and the water will stay longer.