The Drug Foundation is urging drug-users to get illegal substances tested, with warnings of highly potent opioids circulating around the country.
A drug information website - supported by health professionals and government agencies - has already issued warnings about nitazenes, a family of synthetic opioids more harmful than fentanyl.
Drug checking providers have seen concerning increases in nitazenes, which can be deadly at very low doses, being sold as other substances.
Drug Foundation executive director Sarah Helm said the growing prevalence of nitazenes in the community was concerning as they could often be sold as something else.
"These are very potent drugs that can cause overdose and death at very low doses, especially if people don't know that they're taking them.
"We've seen them sold around the country in many different colours and forms including pills, powders, gel caps and liquids. So we are urging people, no matter what they have and how experienced they are, to get their drugs checked if they can."
On Friday High Alert, New Zealand's drug early warning system, said that an orange powder found in Wellington, being sold as butonitazene, was likely to be N-pyrrolidino-protonitazene or N-pyrrolidino-isotonitazene, both substances are more potent and potentially deadly to users.
High Alert says N-pyrrolidino-protonitazene has been reported to be 25 times more potent than fentanyl and has been linked to deaths worldwide.
In September, High Alert warned that yellow tablets being sold online as oxycodone had tested as metonitazene.
Helm says that the increase in nitazenes use means that improving access to naloxone, an opioid overdose medicine, will be crucial to avoid deadly overdoses. Police forces in the United States already routinely carry naloxone on patrol.
"Naloxone saves lives and can reverse a nitazene overdose. We're urging people to get their hands on it if they can, but we need to make it easier to get," she said.
"We are concerned that the variety of forms that these drugs can come in, and the misrepresentation of what the drug is, may mean people with little experience or preparation are at risk.
"Even people who are used to taking opioids are finding themselves in trouble. Because these drugs are so potent, it is hard to measure an accurate dose."
Drug checking is a free, legal and confidential service available at clinics across the country.
Help with alcohol and drugs - in an emergency dial 111
Alcohol Drug Helpline: 0800 787 797