Moves to restrict the sale of herbal highs or party pills to people over the age of 18 have been welcomed by drug experts, retailers and social interest groups.

The new laws - an amendment to the Misuse of Drugs Act put forward by Progressives leader Jim Anderton yesterday - also places controls on marketing and labelling of the products.

The predominant ingredient in the pills is benzylpiperazine (BZP) which is derived from the pepper plant and is legal here.

It is estimated that 5 million party pills have been sold in New Zealand since 2000.

The Drug Foundation said it had major concerns about the legal status of BZP.

The chemical and related substances were left unregulated after the Food Safety Authority declared they weren't a dietary supplement, foundation executive director Ross Bell said.

"The result is that at the moment, BZP could be made in insanitary conditions, mixed with contaminants, or sold to children," he told Parliament's health select committee.

The amendment will control party pills through the addition of a fourth category or Class D to the current drug schedule.

The committee is also considering whether to add other abused substances such as inhalants to the category.

The amendment was also welcomed by the Retailers Association, which said it did not question the need for adequate safeguards against the misuse of drugs.

But individuals were responsible for determining whether a substance should be bought and used for a particular purpose, spokesman Barry Hellberg said.

The National Council of Women said there would always be a conflict of rights when balancing the freedom of expression with the possibility of harm to others.

Protecting the vulnerable was important, even if it curtailed others' freedom said president Christine Low.