More than half the drivers taken to hospital after causing a crash were found to have drugs in their system, a study has found.
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.
Police can only drug-test people if they believe they are under the influence. A blood test is carried out if the driver fails an impairment test.
"We think the majority of drivers driving with illicit drugs are pretty safe from detection, unfortunately," said the AA's Mike Noon.
"They may be caught. But the roadside saliva testing really sends a clear message that if you drug and drive, you could be randomly caught."
But Associate Minister of Transport Simon Bridges said the Government would wait for saliva testing technology to improve before using it.
A government review of the drug testing regime in May concluded the testing devices were not reliable or fast enough to be effective.
It ruled the saliva screening takes at least five minutes, is unlikely to detect half of cannabis users, and results are not reliable enough for criminal prosecution.
"The real factor is reliability ... we can't have innocent people accused of drug driving if they haven't been.
"But as the technology improves, I'm sure in the future we will have a randomised roadside drug test."
Mr Bridges said the new research would be given to the police and Transport Agency to inform the ongoing testing regime.
Another area of concern highlighted by the research was issues with methadone users driving.
"While those on a prescribed stable methadone dosage for treatment should be safe to drive, problems can arise if it is mixed with other impairing drugs, including alcohol."
Drivers with more than the legal limit of alcohol in their system made up just over half of the 453 samples analysed.
Fifty-three per cent of the alcohol group had drugs in their system - with 90 crashes caused by people with both alcohol and cannabis.
The testing showed indications, but not proof, of the use of a drug or one of a drug family.
The presence of a drug in a person's blood does not mean that they were impaired by that drug.