CANNABIS prescriptions could soon be available to Australians for the first time as evidence mounts for its medicinal use in people with cancer and multiple sclerosis.
Australian doctors are testing a cannabis mouth spray called Sativex in cancer patients with pain that does not respond well to painkillers such as morphine.
The phase-three trial is the last of several studies required for manufacturer GW Pharmaceuticals to try to licence the drug in Australia.
Brian Le, a palliative care specialist at the Royal Melbourne Hospital, said four Australian hospitals were taking part in the study, which involves about 300 patients in 20 locations around the world. If the drug is found to be safe and effective, he said it could be available to patients in the next few years.
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.
Dr Le said patients in the trial cannot drive because Australian laws prohibit driving with cannabis in the system.