Associate Health Minister Peter Dunne said the new legislation would come into force by August, when a temporary regime which banned unsafe products would lapse.
He expected it to be a "game-changer".
Asked how officials would define a "low-risk" substance, he said: "These standards will be worked out by health experts and clinicians - not politicians - and that is the way it should be.
"But we are talking about pharmacological substances so there is always some element of risk when people choose to consume them. Individuals can have reactions," he said.
"But ... this legislation is [about] minimising that risk to the greatest extent possible and making things as safe as possible, and that is what the approval criteria will reflect."
Most parties were still considering their stance on the bill, but Labour and the Greens indicated they were likely to support it."
Changes
* Regulatory authority in Ministry of Health to monitor new drugs.
* Committee of experts.
* New offences and penalties of up to two years' jail or fines of up to $500,000.
* Minimum purchase age kicks in.
* Sellers of legal highs restricted.