NZ Drug foundation deputy executive director Ben Birks Ang said he believed those affected bought what they thought was another drug like cocaine but it turned out to be fentanyl.
"Instead of getting stimulated, they had a very strong opioid."
What concerned him was fentanyl or fentanyl-type substances being mixed with other drugs.
"That's what we've seen in North America and in Canada in particular where overdoses spiked in 2016, when MDMA or Ecstasy and their meth supply had become adulterated with fentanyl and fentanyl-like substances.
"So this was a group of people who might be slightly younger, going to festivals and parties taking MDMA expecting to feel more energetic and loving towards each other and instead getting a very strong opioid anaesthetic and dying because of that."
While no further incidents had been reported, there was still a possibility that there could be future issues with fentanyl or fentanyl-like substances.
Birks Ang wanted to make people aware of its effects so they could tell if someone had overdosed as well as advising users to check for fentanyl.
The drug foundation was unsure how the fentanyl came to be sold as another drug and could only speculate unless police found the source.
"It could have been just one batch that came into the country," Birks Ang said.
"There were some of us wondering if this was a mislabelled bag. That people genuinely thought this was cocaine or a cocaine mix."
He hoped there wouldn't be any more cases.
"There is a possibility we might see more from this particular one but we're hopeful it's been contained."
The health sector was trying to prepare for the likelihood of something like the opioid problem in North America coming to New Zealand.
"It doesn't take much for the very small drug supply in New Zealand to be saturated with something else."
Birks Ang said it might only be a couple of batches of a substance like MDMA being adulterated with fentanyl and they needed to make sure to prepare for that with good testing.
The drug foundation was also trying to get more Naloxone in the market, he said.
Naloxone was a drug that reversed the effects of an opioid overdose. It could be injected or used as a nasal spray, but it might take more than one dose depending on the strength of the fentanyl.
"The way it works – there are opioid receptors in the brain and it competes with the drug. It binds on to some of those receptors so the drug itself can't. If they've only taken a little bit extra of the opioid than is appropriate for their body, and they have Naloxone, then that may be enough."
The foundation was also advising people, especially those in rural areas like the Tararua District, to exercise a bit more caution.
"Ideally we'd want no one to take these but some people will and we don't want them to die."
Birks Ang said getting it checked at a drug checking clinic or purchasing test strips to be used at home was the best approach.
He said it was also a good idea to have someone around if they needed to intervene.
Those who were wanting confidential advice could contact the Drug Foundation or visit the website: https://thelevel.org.nz/ They can make contact through direct messaging on Facebook or Instagram as well.
