They are due to appear in Dunedin District Court on Wednesday.
During the operation, police seized drugs valued at up to $330,000, along with a pistol and approximately $20,000 in cash, Detective Inspector Harvey said.
A large amount of the drugs supplied were being sold as MDMA (ecstasy), however some is believed to be eutylone.
Eutylone is a stimulant drug in the synthetic cathinone family and is known to be sold and taken as MDMA as it mimics the effects.
The drug has recently been linked to a number of hospital admissions throughout New Zealand.
Detective Inspector Harvey said purchasing or buying synthetic cathinones (as a pill, capsule or powder) greatly increases the chances of accidental overdose.
"This is because synthetic cathinones are active in lower doses, for some this can be as low as 10mg which is a tenth of MDMA. If someone takes synthetic cathinones in an
MDMA-sized dose, it can have fatal consequences.
"These arrests and the seizure of drugs from this operation will have a
significant effect on supply in Dunedin and will reduce harm."