Dunedin police have arrested eighteen people for drug related offences following a phone monitoring operation.

Twenty one properties across Dunedin and Oamaru were searched yesterday as part of the three month operation.

Six women and twelve men have been arrested and charged with offences ranging from supply of Class A drugs to possession of cannabis.

Police say they're pleased with the outcome, which recovered a large quantity of cannabis and 'magic mushrooms'.

Electronic interception has proved a success in the past, leading to the uncovering of Dunedin's first confirmed meth lab in 2003.

The eighteen people will appear in Dunedin and Oamaru District Court's next week.