He said he was disappointed to see the head of a drug testing agency quoted in media this year as saying employers "certainly don't want someone who's got an addiction problem entering into the workplace".
"I found this a pretty disappointing and counterproductive perspective, and unfortunately indicative of the views of some, perhaps many, around addiction issues.
"Drug testing plays an important role in New Zealand's higher-risk work places, particularly where machinery is involved [and] for the benefit of the individual, their colleagues and the company as a whole.
"But let us not lose sight of the health and safety reasons for it, and not start using it as a de facto law enforcement and punitive measure."
Later today a political panel debated medicinal cannabis reform.
Officials are developing regulations to allow people to access cannabidiol products on a prescription basis, and Dunne said he wanted New Zealand-based clinical trials.
Parliament is likely to next year vote on a member's bill by Green Party MP Julie Anne Genter that would go much further in freeing up supply of cannabis for medical use.
It would amend the Misuse of Drugs Act to make a specific exemption for any person with a qualifying medical condition to cultivate, possess or use the cannabis plant and/or cannabis products for therapeutic purposes, provided they have the support of a registered medical practitioner.
This exemption would also apply to an immediate relative or other nominated person, so they can administer or supply cannabis to the person.
Qualifying health conditions include any terminal illness, any severe chronic disorder of the immune or nervous system, chronic back or other pain, and any other condition a medical practitioner certifies may benefit from cannabis.
The law change has the backing of Labour, the Maori Party, and Act. National is yet to decide how the party will vote on the legislation, or whether it will be a conscience vote.
Dunne had refused to disclose how he would vote, but raised his hand when the panel was asked if they would support the legislation.
After being asked why the pace of reform was so slow, he said both National and Labour were reluctant to move too quickly, and said he needed a mandate to deliver change, which could be delivered after September's general election.
Green Party co-leader Metiria Turei said the issue of drug use was now seen as a health issue, but it was also a human rights issue.
Maori Party co-leader Marama Fox said she was in favour of moves towards decriminalisation of cannabis, but said many Maori were strongly opposed to changing the law because of the harm the drug did to communities, particularly young Maori.
"I've got cousins who are schizophrenic [and] long-term drug users. I've got cousins who have brain tumours, long-term drug users. It is not harmless. And I think if we ignore that part of the conversation then we are not being upfront with ourselves."
If cannabis dealing and use was still illegal, then there needed to be consistency in policing the law, Fox said.
"I could not get a police officer to come to the school when I found out one young man was selling drugs at the school. They didn't even want to talk to him. It's like, what are you going to do?"
