High Alert Drug Information and Alerts Aotearoa New Zealand said tetracaine, also known as amethocaine, had been detected in samples of drugs being sold as cocaine.
"People who consume this powder thinking it only contains cocaine are at risk of serious harm," the agencies said.
Harmful effects of tetracaine were dose dependent, and it could cause ringing in the ears, blurry vision, dizziness and changes in people’s heart rate.
High doses could lead to seizures and cardiac dysrhythmias, which could be fatal.
Tetracaine is commonly used in healthcare as a local anaesthetic and does not produce psychoactive effects.
The contamination in the Dunedin region was discovered after a sample of white powder sold to someone as cocaine was presented to a drug-testing facility in the city.
Preliminary testing by the Institute of Environmental Science and Research (ESR) confirmed that the sample contained both cocaine and tetracaine.
"High Alert urges caution should you choose to use white powders and drug checking is recommended to help minimise the risk."
High Alert suggested if people were going to go ahead and use this substance, to avoid using it alone, start off with a lower dose, avoid using it at the same time as other substances and medications, and that "gumming" a substance would have a slower onset.
People should call 111 and ask for an ambulance immediately if they or anyone else was concerned or had any of the warning signs after taking this substance.
"Tell them what has been taken and that it could contain tetracaine — it could save a life."
— APL
