A festival goer who unknowingly took fake MDMA/ecstasy said the effects lasted 5 days.
Police confirmed 13 users of the fake drug, including a 15-year-old were hospitalised after the Electric Ave festival in Christchurch in February.
On 24 February, Christchurch Hospital Emergency Department reported the admission of a number of people suffering from a 'bad batch of MDMA/ecstasy'.
Police have since established it was N-Ethypentylone - a psychoactive cathinone which is three times stronger than ecstasy.
Detective Inspector Greg Murton said, "The issue for the public is that a dose of MDMA/ecstasy is generally 100mg, however, to get the same effect only 30mg of N-Ethylpentylone is required,".
Deaths have been documented overseas as a result of an accidental overdose of N-Ethylpentyone.
A person, who didn't want to be named, experienced the fake drug and said he and 20 friends couldn't sleep for up to 48 hours and experienced "uncannily similar symptoms."
"I became quite anxious, self-conscious I was really self-aware to the point where I thought everyone was looking at me." He said this then turned into paranoia, accompanied by a fast heart-rate. Some of his friends were still experiencing problems five days later.