The Drug Foundation is worried about a new drug that is being falsely sold as the psychedelic substance LSD.
It said drug testing at the Rhythm and Vines festival revealed some paper tabs sold as LSD were in fact another drug, 25B-NBOH.
The drug was found on tabs of different colours and patterns and had come from more than one region.
Drug Foundation Executive Director Sarah Helm said the strong psychedelic and stimulant and similar drugs had caused hospitalisations and deaths in other countries.
"Because this is a relatively new drug, there isn't much known about its toxicity, but we can take clues from similar drugs, such as 25I-NBOMe, which has caused hospitalisations and deaths worldwide.
"25B-NBOH can be active even at very tiny doses, so it's difficult to dose accurately and may increase your risk of overdose."
The foundation said its test results were confirmed by ESR this week.
The NZ Drug Foundation checked 748 samples at the Rhythm and Vines festival over the New Year period.
"These 25B-NBOH samples prove drug-checking's worth, having clearly prevented serious harm to people who would have otherwise taken them," said Helm.
Helm said the foundation was "very" concerned the drug is likely to be in the community and warned that anyone who had purchased what they believed to be LSD to be careful.
If someone has taken a tab that might be 25B-NBOH and experiences symptoms including severe agitation, anxiety, or psychosis, vomiting, abnormal heart rate, seizures or passing out, call 111 or get medical help as soon as possible.