WELLINGTON, March 14 (Reuters) - New Zealand party goers bought up stocks of legal stimulants on Friday, a day after the country banned the use of an ingredient in the so-called party pills.

The parliament passed a law on Thursday classifying the active ingredient in the pills, benzylpiperazine (BZP), the same as cannabis, and giving retailers until April 1 to dispose of stocks.

The pills, which go by such names as Frenzy, Torque and D-lite, have been legal and have been touted by their supporters as keeping their users away from hard drugs, while being safer than alcohol and tobacco.

The industry group of party pill makers and distributors said the ban would drive them underground.

"A lot of party pill users will continue to use them or seek out illegal drugs," Matt Bowden of the Social Tonics Association told Radio New Zealand.

He said the pills were not addictive and had never caused a death.

Health professionals and some social groups had pushed for the ban after several cases of users suffering bad effects and falling into comas after mixing the pills and alcohol.

"This is the determination of expert toxicologists, doctors, and other specialists," said the ban's architect, Associate Health Minister Jim Anderton in a statement.

Costing up to NZ$40 ($32) for a pack of four, the pills have been widely available in service stations and convenience stores.

An amnesty until Oct 1 has been announced for anyone caught with the pills, after which possession could see users facing fines or up to three months in prison.

The pills were developed around 10 years ago and BZP was derived from chemical drenches used to kill bowel parasites in cattle.

The BZP-based pills are already banned in several countries including Australia, Denmark and the United States. (Reporting by Gyles Beckford; Editing by Sanjeev Miglani)

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