A justice group is warning synthetic drugs will keep killing New Zealanders unless the government changes their thinking.

The comments follow a rise in hospitalisations in Christchurch, including one death.

Two of the 19 people admitted over the past two weeks are still fighting for their lives in ICU.

Transforming Justice Foundation co-founder Scott Guthrie says the trouble is synthetic drugs are hard to test for.

"The make up changes on nearly a weekly basis. It's out of control. People just put whatever they want in there."

He says we already have a synthetic drug crisis in this country.

"The use of synthetic drugs is just going to be more prevalent by the week, and we're just going to see more people dying."

Guthrie is calling on the government to implement mandatory random drug testing for beneficiaries and in the workplace, but says drug users also need to be made responsible for their actions.