For example alcohol is legal, but more harmful than illegal drugs cannabis, LSD and ecstasy.
"In 2016, an estimated quarter of a billion people used currently illegal drugs, while about 11.6 per cent of these are considered to suffer problematic drug use or addiction."
Speaking at the report's release, Clark said decriminalising drugs was somehow the "hardest of all issues".
"Why is this? I think it comes back to the problem of the UN conventions, the problem of these certain categories of drugs being seen as criminal activity if you use them. It follows from that that there's a narrative that says bad people do these things because it is criminal.
"If you're a person using drugs, you're a bad person because you're breaking the law and therefore there will be punishment. Actually the use of drugs requires a health and safety approach, a social policy approach, a safe spaces approach."
NZ Drug Foundation chief executive Ross Bell said there was a discrepancy in New Zealand in terms of how illegal a drug is and how harmful it is.
Drug policy has been a political football in New Zealand, he said.
"Talking about law reform is a risk of being seen as soft on drugs. But if people would rather their loved one gets help rather than be punished, why is this still a political football?"
He urged New Zealand to follow Norway, which recently decided to follow Portugal's example and decriminalise drugs, while adding treatment and education resources.
A Drug Foundation report showed that $273m a year was being spent on drugs in the criminal justice system, while $78m was spent on health services.
The latest Corrections Department numbers from September 2017 show about 1400 of the 10,470 prisoners were in prison because of drug-related or anti-social offences.
"Why do we have so many people in prison for drug offences? Why are we building prisons and not spending more money on treatment?," Bell said.
He was encouraged by successive governments talking about treating drug use as a health issue, rather than a criminal one.
"It started to happen under the previous Government. [Sir] John Key's methamphetamine plan, in the early days, all of that went to meth treatment. This Government has to build on those things."
Bell pointed to the Te Ara Oranga pilot programme, which is a partnership between police and the Northland DHB to reduce methamphetamine harm (see below).
He said there are reasons for optimism.
"Medicinal cannabis, the referendum on personal use of cannabis, the promise of money going into drug treatment, the mental health inquiry that will be a good vehicle to expose weaknesses in addiction treatment, the Law Commission recommendations to replace the Misuse of Drugs Act.
"Fundamentally we are on the right track."
Pilot programme making inroads
A pilot programme in Northland to treat methamphetamine use as a health issue has already seen more than twice the number of users sent to treatment rather than the courts.
Te Ara Oranga, which has been running for three months, is based on ensuring users are given access to treatment while directing justice resources to the most significant criminal activity.
Northland DHB communications manager Liz Inch said the programme tackled methamphetamine use through a combination of treatment, education and community help.
"We can't arrest our way out of this problem."
In the pilot period, the police methamphetamine team has referred 24 people for treatment and arrested only nine people - mostly for manufacture and supply offences. It has also executed 12 search warrants, seized 13 firearms and received two reports of concern for children.
"They are offering treatment as a pathway before the courts, unless it's appropriate for the person to be arrested," Inch said.
The $3 million in funding for the programme comes from money secured through the Criminal Proceeds (Recovery) Act.
It includes a programme called Employment Works to help people with drug and alcohol or mental health issues into work.
It has had 50 referrals in three months and put 15 people into work, prevented two people from losing their jobs, and helped five people into job training.
Other initiatives include providing screening tools for GPs so they can refer people to treatment, and a social media campaign that has seen 61 calls to a drug and alcohol helpline.
The pilot has also funded a voluntary one-day education programme that has taken place six times and seen 51 people attend from 120 referrals. Thirty-five people have indicated behavioural change.
The pilot is also gathering methamphetamine-related data that did not exist before. DHB clinicians have managed 71 clients since October.
"We didn't collect that information before, so that will now help with evaluation and reporting," Inch said.
