The Government has moved to toughen up the animal-testing regime for party pills.
MPs are debating the Psychoactive Substances Bill, which requires manufacturers to prove that legal-high products are safe before sale.
Associate Health Minister Todd McClay says it is necessary for some testing to take place in order to ensure human safety.
Under the bill as it stands, manufacturers could only use animal testing if other options were not available.
But in a last-minute change on Tuesday, Mr McClay proposed that the availability of alternative testing options be reviewed annually as a way of strengthening the regime.
The Green Party wanted to block the use of data gained from animal testing to prove a product is safe.
However, that amendment was defeated with opposition from National and independent MPs Peter Dunne and Brendan Horan.