The coroner is investigating about 20 deaths possibly linked to synthetic drugs.
The drugs, linked to deaths in the last two months, contain a notoriously dangerous chemical manufactured overseas.
Police have confirmed AMB-FUBINACA has been found in synthetic drugs tested by the Environmental Science and Research Crown Institute (ESR).
Chief coroner Judge Deborah Marshall said since issuing a public warning in July, the office was now reviewing around 20 deaths.
That was up from the previous count of 11 deaths.
However, some cases initially thought to be associated with the drugs have been removed after post-mortems found the drugs were not the cause, Judge Marshall said.
A forensic chemist at ESR, Kevan Walsh, said AMB-FUBINACA was nicknamed a zombie drug because it could be 75 times more potent than the active ingredient in natural cannabis, THC.
Mr Walsh said in samples from drugs linked to people who had died, as well as from police raids, AMB-FUBINACA was the most commonly detected chemical.
Last week, a 21-year-old Feilding man died and four others were admitted to Palmerston North Hospital after taking synthetics.
Ten deaths in Auckland in the last two months have also been linked to synthetics.
MidCentral DHB spokesperson Richard Barrass said users behaved unpredictably and posed a risk to themselves and others.
St John ambulance service said staff had attended 691 incidents believed to be related to the use of synthetic drugs since June.
Detective Inspector Scott Beard said the chemical was being smuggled into the country and mixed with plant material to make the drug.
Police have made several recent arrests linked to the drug's manufacture and sale, but Mr Beard did not know whether they were making any progress in stopping its distribution.
Police urged anyone who knew of people selling or manufacturing synthetic drugs to get in touch.