The NZ Drug Foundation (NZDF) drug-tested a white lolly found in a Rinda-branded pineapple sweet after a person complained of a sour taste and "feeling unusual" after trying them.
They found the lolly contained around three grams of meth.
"A common dose to swallow is between 10-25mg so this contaminated lolly contained up to 300 doses," NZDF executive director Sarah Helm said.
"Swallowing that much methamphetamine is extremely dangerous and could result in death."
The lollies were distributed by the Auckland City Mission after they were donated as part of food parcels.
Auckland City Mission chief executive Helen Robinson said she was devastated.
They believe 300 to 400 people might have received the parcels, and work was underway "with urgency" to contact them.
"The mission only accepts commercially manufactured food ... and the lollies appeared as such when they were donated," she said.
"It was a highly appropriate thing for our staff to believe this was a safe lolly. It was in a sealed, contained package and the lollies were individually wrapped."
Ms Robinson said she knew of eight families affected. No illness or injuries have been reported.
The NZDF said the discovery of the lollies justified their legalised drug-checking system and communication networks.
Deputy director Ben Birks-Ang said more lollies could be out there, suggesting they may be part of a botched drug trade.
"We know that disguising substances as something else to smuggle it is common internationally," he said.
With AAP.
