The Automobile Association believes the number of road crashes due to drivers being impaired by prescription drugs is much higher than is acknowledged.
The association says a recent Environmental Science Research report identified a significant number of drivers who died in crashes had prescription drugs in their system, as well as alcohol and/or other drugs.
AA general manager of motoring affairs Mike Noon says there needs to be a greater warning from doctors when they prescribe medicines.
Mr Noon says they need to particularly warn about the combination of prescription drugs and alcohol, as the effect varies depending on the metabolism of each driver.
