The finding comes after toxic industrial chemical methylenedianiline was found this month being sold in place of MDMA in Auckland.
Know Your Stuff warned that chemical has been linked to several poisoning cases in Auckland where the patients suffered liver damage.
Cathinones are a family of stimulants often sold in place of MDMA.
Know Your Stuff deputy manager Dr Jez Weston said it was likely used as MDMA simply because they it was available on the illicit market.
They had found the substitute in testing right across the country, and they were already seeing more than last year, Weston said.
They'd found cathinones in both pressed pills and crystal form.
The more common ones found in New Zealand include N-ethyl pentylone, mephedrone and eutylone.
On rare occasions methylone, mexedrone, 4-methylmethcathinone, MDPV, and Alpha-PVP have also been found.
Cathinones are usually more potent than MDMA, so what a person might think was a manageable amount could end up being dangerous.
Cathinone effects last between two and five hours, but after-effects - including sleeplessness - generally last in your body between six and 24 hours.
Redosing will extend these after-effects.
One person who presumed they had weak MDMA and took several doses experienced what they called "48 hours of hell" from what turned out to be eutylone.
There was no way to visibly tell the difference, and Know Your Stuff recommended for people to visit their testing sites if possible, or buy their own reagent tests.
"Cathinones are incredibly dangerous, and we'd rather see you regularly in the checking tent summer after summer than in hospital even once," Weston said.
"We'll be busy this summer at festivals up and down the country and looking forward to being more open and public about what we are doing."
Pill-testing law
Health Minister Andrew Little's Drug and Substance Checking Legislation Bill passed earlier this month.
The bill changes two pieces of legislation - the Misuse of Drugs Act and the Psychoactive Substances Act to allow people to get their drugs tested at festivals without prosecution and permits event organisers to host testers.
The bill will automatically expire in 12 months, with Little committing to bringing in a permanent change which will go through the full parliamentary process before then.
The law change came too late to allow Know Your Stuff to effectively test our summer festivals.
Wendy Allison told RNZ that there was not enough time to import the specialist spectrometer equipment needed to test at all festivals.
The organisation had just three sets of equipment, meaning they could only attend three festivals at once, Allison said.
"There are far more events than that happening, especially around the New Year's period."
She said there were other spectrometers in New Zealand, but they were hidden away in laboratories.
"The ability to cut through all that red tape in the time we have would be very limited."
The spectrometers are manufactured in Germany, and took six weeks to arrive when the organisation ordered them last year.
"That was of course pre-Covid and not over a holiday season. So I would expect, if we ordered spectrometers tomorrow they would arrive in February at the earliest."
Allison did not blame the Government for the delays in the legislation, instead putting it down to outside influences such as Covid-19 and other political parties opposing the law last year.
She said the legislation would help improve the service they could offer, because it allowed volunteers to handle the substances, making it more efficient.
Before the legislation, the group had to instruct festival-goers to test the drugs themselves, because it feared volunteers would be at risk of prosecution if they handled substances.
"It's not a complete washout. We are limited in the number of events we can attend, but we will be able to help more people at those events."
