A spokeswoman for Novartis, the company employed by GW Pharmaceuticals to commercialise the drug in Australia, said it was working with the Therapeutic Goods Administration to make Sativex available to patients with multiple sclerosis who suffer from uncontrolled muscle spasticity.

No pharmaceutical drugs based on cannabis are currently licensed for use in Australia. Since 2004, health authorities in Britain, Canada and Spain have licensed Sativex for patients with multiple sclerosis, a neurological condition that causes painful muscle stiffness in about 90 per cent of sufferers.

While cannabis is known to cause hallucinations and delusions, Dr Le said phase-one and phase-two trials of Sativex in more than 400 cancer patients found it relieved pain with few side effects, the most common being nausea. He said psychiatric side effects were very rare in the doses used and that patients did not report feeling ''stoned''.

''Our experience is that pain improves and the patients actually feel better. They're more able to do daily activities, sleep better through the night without pain and think clearly, so instances of feeling confused or out of it are low,'' he said.

Dr Le said the drug worked by targeting cannabinoid receptors in the brain. ''Cannabinoid receptors are like morphine receptors in the body, they mediate how the pain is sensed and how that pain message is transmitted to the brain and therefore perceived, so it reduces the conduction of that message to say there is pain occurring,'' he said.