Detective Inspector Anna Grant said police were continuing to investigate the matter as a priority, given the risk to the public.
“This includes working to identify if the cases are connected, and find out where the supply has originated,” she said.
The suspected overdoses have occurred across the wider Wellington area, including Miramar, Brooklyn, Johnsonville, Upper Hutt and Wainuiomata.
The substances involved are suspected to include GHB or GBL. GHB is also known as “fantasy” or “liquid ecstasy”.
RNZ reported the fatal Brooklyn incident is understood to have happened at Woofington’s, a castle-like mansion in Wellington’s hills.
The property was the subject of a recent TVNZ+ documentary series, What the Hell Happened at Woofington’s?
GHB, GBL and 1,4-BD – what are they?
NZ Drug Foundation executive director Sarah Helm said there had been a recent increase in people taking “G” substances.
“G” substances refer to GHB, GBL and 1,4-BD.
The drugs can produce a euphoric, relaxed or sleepy high, but can also cause serious harm.
Negative side effects can include blurred vision, slurred speech, loss of co-ordination, memory loss, panic attacks, tremors, heart palpitations, loss of consciousness, psychosis and death.
GHB is often sold as a clear, oily liquid or, less commonly, as a white powder that is dissolved in water or juice.
GBL, or gamma-butyrolactone, and 1,4-BD, or 1,4-butanediol, are found in industrial chemicals used to produce polyurethane, pesticides, elastic fibres, medicines, coatings on metal or plastic, and other products.
Once consumed, GBL and 1,4-BD rapidly convert to GHB in the body.
According to Know Your Stuff, GBL can take effect faster than GHB and is stronger, increasing the risk of overdose.
The drugs take about 15 to 45 minutes to take effect and can last up to four hours.
Inspector Wade Jennings on Friday urged the public to “exercise caution” with drugs of this type.
“Anyone who may have this type of substance is urged not to consume it.”
People have been advised to go to their nearest healthcare provider urgently if they are feeling unwell.
In August last year, four people were arrested after nearly 2000 litres of GBL was seized at the border.
The product had an estimated street value of $14 million, according to police.