The Ministry of Transport study used blood samples taken from 453 drivers who caused crashes.
Drugs were detected in the systems of 258 drivers, analysis by the Institute of Environmental Science and Research (ESR) found.
Of that group, 156 were found to be on drugs not administered by a medical professional
Ninety people sent to hospital had both cannabis and alcohol in their system.
Yesterday, the Automobile Association renewed its calls for random roadside saliva tests to be used to target drug drivers.
Such saliva screening devices can detect only three drugs – cannabis, methamphetamine and Ecstasy – and are used in every Australian state.