Operation Nest, an organised crime operation focusing on the misuse of prescription medication and property, has been running for more than a year.
Police undercover agents have been used in Oamaru over recent months as part of investigative methods.
Nine of the arrested are from Oamaru and the rest from the greater Auckland area and Whakatane.
More than 60 police staff were deployed across the country yesterday, with 44 in the Oamaru area, sourced from South Canterbury, Dunedin, Central Otago and Waitaki, supported by staff from the Customs Service.
Charges were still being finalised and Detective Sergeant Mike Ryder expected a ''significant number'', relating principally to dealing in class B controlled drugs and prescription medications morphine, ritalin and methadone.
Three Oamaru men appeared before the registrar in the Oamaru District Court yesterday in connection with the operation.
Two were remanded to appear on December 8 and one was remanded to appear today.
More were expected to appear in court today.
The operation represented the culmination of a significant operation that had put pressure on Waitaki resources, but police hoped it would reduce the availability of illegal drugs locally, Det Sgt Ryder said.
Yesterday did not represent the end of Operation Nest and there was still a lot of work to do locally. Police still had a lot of people to talk to.
A significant quantity of medication had been recovered, although tallies were still to be done.
Where the medication came from would come out in court, he said.
Southern crime services manager Detective Inspector Steve McGregor said the significance of yesterday's results would have a bearing on the abuse of controlled drugs in the Waitaki district.
