Drug dealers have been offering a free dose of heroin to customers who buy three doses of methamphetamine, known as P, according to the Police Association.
The June edition of the association's magazine, Police News, reported suppliers were recommending the heroin as a way to "take the edge off" the comedown from a P binge.
The information was part of a series the magazine has been running on the problems of organised crime.
A year ago the magazine warned of a resurgence in "homebake heroin" use - some users were looking for an alternative to methampetamine, in the hope of escaping the clutches of violence and intimidation that went along with the P trade.
"At the same time, some in the organised crime-controlled drug trade were looking to diversify by cultivating a new market for heroin among their regular P customers.
"Information passed to us suggests some methampetamine suppliers have even offered a 'free' dose of heroin to customers buying three 'points', or doses, of P, recommending it as a way to 'take the edge off' the comedown from a P binge," the magazine said.
For now most of the available street heroin in New Zealand appeared to be manufactured from diverted prescription drugs.
"With international heroin prices at historic lows, street product in many parts of the world is now of reliably high enough purity to smoke or snort, rather than injecting the drug.
"This makes it more marketable to users accustomed to smoking or snorting drugs like methampetamine," the magazine said.
"Other overseas trends points towards combined use of P and heroin as a highly potent speedball."
The magazine said there was real cause for alarm that with heroin able to be sourced from the same overseas markets as methamphetamine precursors, organised crime would move quickly to supply any new market for the drug in this country.
Meanwhile, another new party drug, thought to have been linked to several deaths in Britain, is now circulating in New Zealand.
Mephedrone (4-methylmethcathinone) is known as "meow meow," "MMCAT", "drone", "bubbles" or "plant food", comes in the form of white powder, crystals, capsules and pills.
Despite several customs seizures of the drug there is little evidence of widespread use in New Zealand to date.
National Drug Intelligence Bureau coordinator, Detective Inspector Stuart Mills, said 815 grams was found in 29 seizures between September 1, 2009, and March 31.
Most of the importations were sent from Britain and were destined for addresses in Auckland, Dunedin and Central Otago.
The feelings caused by mephedrone are said to be similar to those caused by cocaine or amphetamines.
