Driving 'stoned' increases the chance of having an accident by up to 300 percent, according to a research review by UNSW's National Cannabis Prevention and Information Centre (NCPIC).

A new national poster campaign - "Smoke and drive and you're as good as drunk" - is being launched this week to highlight the risks .

The poster, produced by NCPIC and funded by the Federal Government, will be distributed across the country through law enforcement, health and education sectors.

The Centre's Professor Jan Copeland said it was important for the community to have evidence about the impact of smoking cannabis on driving because there continued to be the perception in the community that there were few risks.

"Cannabis users tend to drive more slowly and so erroneously believe that they are driving more safely.

"People use cannabis to alter their perception. The one place you don't want to have your perception changed is behind the wheel of a car," Professor Copeland said.

Smoking cannabis reduces reaction time as well as the ability to make decisions. The latest review of evidence shows that driving under the influence of cannabis appears to increase the risk of motor vehicle accidents by a factor of two to three times.

"We hope that the poster and accompanying message will alert cannabis users to the potential dangers associated with getting behind the wheel after using the drug," Professor Copeland said.

"The message is clear: if you've smoked cannabis, don't drive."

For more information about cannabis and its effects visit the NCPIC website.

Media contact: Paul Dillon | 02 9385 0226 | p.dillon@unsw.edu.au