Cannabis may become 'the aspirin of the 21st century'

Cannabis, the third most popular recreational drug after alcohol and tobacco, could win a new role as the aspirin of the 21st century, with growing evidence that its compounds may protect the brain against the damaging effects of ageing.

Although the drug distorts perception and affects short-term memory, it may also help prevent degenerative diseases such as Alzheimer's, Parkinson's, Huntingdon's and motor neurone diseases. Scientists at the Institute of Neurology in Queens Square, London, say the "huge potential" of cannabis compounds is emerging, as understanding of its biological and pharmacological properties improves.

Professor Alan Thompson and his colleagues wrote in Lancet Neurology: "Basic research is discovering interesting members of this family of compounds that have previously unknown qualities, the most notable of which is the capacity for neuroprotection."

The results of two trials in patients with multiple sclerosis are expected this summer and the first cannabis-based medicines are being considered for licensing. None of them will have the psychoactive properties of the raw drug when smoked or ingested.

Professor Thompson's team says: "Even if the results of these studies are not as positive as many expect them to be, that we are only just beginning to appreciate the huge therapeutic potential of this family of compounds is clear."

Cannabis was thought to affect the cells like alcohol by seeping through the cell membrane. But in 1990 the first cannabinoid receptor was found, which revolutionised the study of cannabinoid biology. The discovery revealed an endogenous system of cannabinoid receptors, similar to the opioid system, to which the drug bound when it was ingested. Just as endorphins are the body's natural equivalent of heroin, a fatty acid called anandamide (Sanskrit for "inner bliss") is the natural equivalent of cannabis.

The natural system of cannabinoid receptors plays a role in maintaining the balance of chemicals in the brain which regulate the rate at which neurons fire. By altering this system, scientists believe it may be possible to slow or prevent the process of brain decay. David Baker, lead author of the Lancet review and senior lecturer at the Institute of Neurology, said: "Alzheimer's disease is the result of very slow degeneration caused by the death of nerve cells. We probably don't see symptoms until 30 to 40 per cent of the nerve cells have died. Something regulates this decay and if we could slow it by even a small fraction we might delay by a decade the point where someone loses their memory."

But cannabis is a double-edged sword, with potentially damaging side effects. "It may be possible to develop drugs that allow selective targeting of different areas of the brain and spinal cord and there may be a way of limiting the negative effects," Dr Baker said.

A study by Dr Baker and colleagues, in which the natural system of cannabinoid receptors was removed in mice, showed that the rate of nerve loss was increased, indicating its role in preserving brain function. The study, which has been accepted for publication in a medical journal, "really clinches the argument", Dr Baker said.

He added: "Cannabis has gone from the drawing board into trials in record time, largely because of patient pressure. Hopefully it will work and be acceptably safe."