Users on the forum tripme.co.nz said the pills did not appear to contain MDMA - the main ingredient in Ecstasy - but chemicals from a family of hallucinogenics called 2C.
"Them b******s pressing 2CX into street pills is what doomed everything.
"We were living a pill-friendly, take-it-or-leave-it type of country for quite a while before people ended up in hospitals, tripping balls, wondering why they aren't feeling strimmed or chatty," one wrote.
University of Otago student Andy told the Herald on Sunday the seized pills were a hallucinogenic or "trippy" type, different from traditional Ecstasy.
He said they cost $60 each in Dunedin. "I started uni in 2009 and they were around then, but seem to have become more available over the three years spent here," he said.
The new pills were more similar to LSD. "They start by altering your visual perceptions, making things look strange, such as patterns starting to move," he said.
"However, other effects start in which can be very intense. Social situations can suddenly become scary and the user may start talking gibberish, situations become confusing and they may become scared because they cannot control themselves tripping out."
He found the experience terrifying. "Things slowly come back to being manageable about four or five hours after tripping, and sleep is difficult until the next night," he said.
Drug experts warn the bust could spark a price rise and more-toxic pills flooding the streets.
Ross Bell, executive director of the New Zealand Drug Foundation, said there could be "a lot of opportunists trying to cash in on what they might see as a big gap in the market". Massey University drug researcher Dr Chris Wilkins said Ecstasy users might pay more for their pills in the future.
"When supply becomes tight there are usually two ways in which dealers respond. The price goes up and they start cutting their products with other stuff, so the potency and quality goes down," he said.
"But the recent arrests could prove to be a circuit-breaker in the supply of Ecstasy and some users may take the opportunity to give it up."