High Alert Drug Information and Alerts Aotearoa New Zealand said a synthetic hallucinogen called 2C-B was detected in Dunedin and was being sold as MDMA.
The powder presents as a pinkish/purple powder and had both stimulant and hallucinogenic effects.
"2C-B dosages are far smaller than the typical MDMA dose, meaning people consuming this substance believing it to be MDMA could inadvertently consume multiple doses.
"It has a significantly different nature and intensity of effects depending on the dose and route of administration", the High Alert website said.
A third year University of Otago student, who declined to be named, bought what she believed to be MDMA for the Palmerston Winter Solstice festival held on Saturday.
"I got the [MDMA] checked last week and found out it contained 2C-B — I’ve personally never heard of it."
The student said she did not regularly get her drugs checked, but was a bit "sceptical" about what she had because of the purple tinge of her supposed MDMA.
"I’m tossing up whether to take it, but this isn’t my first rodeo with getting fake MDMA from Dunedin dealers. I find taking a low dosage when I’m not sure usually ends up fine", she said.
"... I know some people out there would just not take it, but I spent my petrol money on it.
"If things make a turn for the worst, my group does have someone going sober to babysit us and get us help if we need."
High Alert said at high doses 2C-B was a powerful hallucinogenic and adverse effects could include anxiety or paranoia and a racing heart.
Other reported effects included hallucinations, restlessness and agitation, confusion and disorientation, euphoria, feeling energised and alert and increased empathy and connection with others.
High Alert said if someone was feeling anxious or depressed before taking 2C-B, they would be more likely to have an unpleasant experience.
"Your mindset and the environment you are in can significantly affect your experience on psychedelics — high stimulus settings can quickly become overwhelming."
High Alert said to call 111 and seek help immediately if after taking 2C-B, you started feeling extremely agitated, anxious, paranoid or manic for longer than 15 minutes, had distressing hallucinations, started having suicidal thoughts, a racing heart or having tremors, convulsions or seizures.
