SMOKERS have nicotine patches and heroin users have methadone but cannabis users have little choice except to go ''cold turkey'' if they want to kick their habit.

However, researchers at the University of NSW hope a cannabis-based mouth spray, prescribed to multiple sclerosis sufferers and not available in Australia, could be used to help people quit marijuana.

There are no products aimed at easing people off cannabis, the only option being rehabilitation where a cocktail of prescribed drugs is used to counteract withdrawal symptoms.

But a drug, Sativex, which is a mouth spray, contains two of the main cannabinoids found in the cannabis plant; tetrahydrocannabinol (THC) and cannabidiol (CBD).

It was the combination of both that gave Sativex potential, said Jan Copeland, who is leading the world-first study through the university's National Cannabis Prevention and Information Centre.

''The smoked cannabis available on the market has had almost all the CBD taken out of it, which is almost considered the 'good' cannabinoid, while THC is associated with getting stoned,'' Professor Copeland said.

''The good thing about Sativex, it returns CBD to the compound, and in treating symptoms of withdrawal it can dampen down the effects of THC on the patients' receptor systems without them getting stoned.''

The mouth spray, which the university has been authorised to use, would be given in low doses in a monitored environment every six hours, she said.

Disrupted sleep, difficulty functioning and anger were common withdrawal symptoms and the main cause of relapse, Professor Copeland said.

A former cannabis smoker, Teresa Ursich, said she wished a drug such as Sativex had been available when she was trying to quit. She has written a book about her experience, But It's Only Pot, and has been drug free for seven years. A user for 14 years, she tried going ''cold turkey'' several times before she went into rehab.

''In rehab they give you all these drugs. The major drug they give to you is Valium, and they give you other drugs for the cramps and codeine for the pain. I'm lucky I didn't get addicted to Valium.''

There was a perception that cannabis was a ''soft'' drug, she said, and easier to stop using. ''But the pain is not just mental,'' the 42-year-old said.

''You feel agitated and so sick; you get to a point where you would rob your own grandmother to get some.''