"Users are reporting some pretty bad experiences," NZ Drug Foundation executive director Ross Bell says.
Hospital emergency departments and frontline police are training to deal with the drug's rising popularity.
The thrill for partygoers includes increased energy and hyper-alertness that can last for several hours.
It can also result in nose bleeds, vomiting, blurred vision, fits, convulsions and heart attacks.
When mixed with alcohol or other drugs, it can also spark violent outbursts, exacerbated by hallucinations, and bouts of paranoia and delusions.
Mephedrone was banned by the UK Government in 2010 after legislation was rushed through when it was blamed for the deaths of several young users.
Around the same time, it arrived on New Zealand shores, distributed through gangs.
"We alerted the troops (frontline police) that there was new stuff out there and the type of impact it had on people, what it can do to people," National Drug Intelligence Bureau (NDIB) co-ordinator Detective Inspector Stuart Mills told APNZ.
"It's coming into the country in smaller lots - personal baggage, through the mail centre, or concealed in consignments, which is always very difficult to trace."
Last November, a big police sting, Operation Ark, smashed an Auckland criminal syndicate converting the imported drug into party pills.
Two police staff, a prosecutor, and a millionaire businessman were among 19 people arrested in the long-running investigation.
The maximum sentence for dealing mephedrone, a class C drug, is eight years in prison.
But police say their main concern is that clubbers don't know what they are buying.
"A real danger is people take them, nothing happens, so they take another one, and put themselves in danger, or can't control themselves and put others in danger," said Mr Mills.
Police concerns are shared by health and drug experts, especially given the lack of research into meow meow's long-term effects.
However, new research published this week showed mephedrone use can cause lasting brain damage.
A University of Sydney study examined the effects of daily mephedrone injections in rats over 10 days.
"We found a substantial memory impairment in animals that had been given the higher dose of the drug," lead author Craig Motbey says.
"This is concerning because it confirms earlier hints of memory problems in human mephedrone users. The fact the impairment was still there many weeks after the end of the drug treatment suggests that this damage may be permanent."
Users frequently re-dose throughout a mephedrone session, often continuing until supplies of the drug are exhausted, Mr Motbey says.
The NZ Drug Foundation agrees. Mr Bell said users had reported the drug being "very moreish", resulting in strong cravings.
"People are using these drugs as an ecstasy replacement, but the result is very different. They're more like an amphetamine, rather than the loved-up feeling of ecstasy," he said.
"Frustratingly, people are still quite happy to use these products while being completely naive to the risks."
The facts
WHAT IS MEOW MEOW?:
Class-C drug mephedrone. Its chemical formula is one molecule different to ecstasy.
ALSO KNOWN AS:
Bubbles, drone, white magic.
HOW IS IT SOLD?:
The white, off-white or yellowy powder is used to make ecstasy pills or tablets and is being sold by criminal gangs or groups for between $40 and $90 per pill.
AND THE DANGERS?:
It can cause elevated heart rate and blood pressure, tremors and convulsions, memory loss, paranoia and depression. It has been linked to more than 100 deaths across Europe.Fears latest party high can cause brain damage
