The Government is seeking public feedback on ways to improve roadside drug-testing, including what drugs should be tested for and what the penalties should be.

The announcement today, by Police Minister Stuart Nash and Associate Transport Minister Julie-Anne Genter, follows pleas for swifter action from families of people killed in crashes by drivers high on drugs.

Analysis of blood samples from drivers killed in crashes between January 2014 and May 2018 showed 29 per cent had used alcohol, 27 per cent had used cannabis, 10 per cent had used methamphetamine and another 15 per cent had used other drugs.

Over the same period, blood samples of drivers stopped by police and determined to be impaired by drugs showed 59 per cent had used cannabis and 41 per cent had used methamphetamine.

Of the drivers caught drink-driving in New Zealand, more than a quarter also tested positive for recent cannabis use.

Research done for the New Zealand Transport Agency's Substance Impaired Driving Project also found that 25 per cent of all prescriptions issued in New Zealand were for medication that could impair driving.

Genter said the current law made it hard for police to carry out the high number of tests needed to act as a deterrent.

Testing for drugs was also limited to the presence of legal or illicit drugs, not whether a driver was impaired.

"A considered approach to developing enhanced drug driver testing will mean we can develop a robust testing system that's grounded in evidence and best practice. We need to do this thoughtfully," Genter said.

Nash said 71 people were killed last year in crashes where a driver was found to have drugs in their system which could have impaired their driving.

"Irrespective of whether someone is impaired by alcohol, medication or recreational drugs, they shouldn't be behind the wheel," he said.

A discussion document was signed off by Cabinet last year but its release was delayed because of the Christchurch terror attacks in March, Deputy Prime Minister Winston Peters told Parliament last week.

The public will have until June 28 to have their say on the document, which is seeking feedback on:

• The methods that could be used to screen and test for drugs

• The circumstances in which a driver should be tested

• What drugs should be tested for

• How an offence for drug driving should be dealt with by police

Christchurch mother Karen Dow was joined by other families at Parliament earlier this week to meet National leader Simon Bridges and some of his MPs to discuss the issue.

Among them were the families of Ian Porteous, 80, his wife Rosalie, 76, his sister Ora Keene, 84, and friend Brenda Williams, 79.

The four died in a head-on crash with Jeremy Thompson, 28, his 8-week-old daughter Shady and Nivek Madams, the 8-year-old daughter of Thompson's partner Ani Nohinohi.

Nohinohi was the sole survivor of the crash at Waverley in Taranaki in June last year.

A coroner's inquest last week into the Waverley crash, at the time one of the country's worst, was told that Thompson and Nohinohi had been smoking synthetic cannabis before the crash.

Dow's 23-year-old son Matthew was killed in a crash with a woman who had been drinking and taking drugs before she got behind the wheel near Nelson on New Year's Eve 2017.

Dow presented a petition calling for random roadside saliva testing to Nelson MP Nick Smith last week but the petition was reopened for a week to seek more signatures.

Dow said she was devastated to hear about the inquest into the Waverley crash.

"There's an epidemic in New Zealand and it's a complete lottery on our roads. It could have been any one of us."

At present police can drug-test only drivers they suspect of consuming illicit or legal drugs. The only test available here is impairment testing such as walking in a straight line or standing on one leg. A blood test can then be sought.

Saliva testing is done in jurisdictions overseas, although there are questions over the accuracy of some.

They also have their limitations in that they cannot measure impairment, nor test for the presence of synthetics and designer drugs.

Oral swab tests are expensive, $20-$45 each compared with a few cents for an alcohol breath test.