A group of people hospitalised after taking drugs in Christchurch last month "posed a danger to themselves" because they took a much stronger batch of drugs than they believed they were.
Thirteen people, including a 15-year-old, were hospitalised on February 24 after taking what they thought was MDMA or ecstasy.
Tests have shown what they actually took was N-Ethylpentylone, which is far more potent, police say.
""The issue for the public is that a dose of MDMA/ecstasy is generally 100mg, but to get the same effect only 30mg of N-Ethylpentylone is required," Detective Inspector Greg Murton says.
"Hence, if N-Ethylpentylone is mistaken for MDMA/ecstasy, the user will be taking three times the prescribed dosage, posing a danger to themselves."
The 13 arrived at hospital in an agitated state, with dangerously high blood pressure and an elevated heart rate.