Searches by police, Customs and Medsafe have led to three arrests and the seizure of illegal drugs in three l cities.
Police say Operation Adder this week centred on a group suspected of importing illegal performance enhancing drugs, used in high performance sport.
The operation involved searches at properties in Auckland, Hamilton and Christchurch.
Police say the illegal drugs and prescription medicines were repackaged or pressed into pills, then sold to customers throughout the country.
Drugs, a large sum of cash, and a pill press capable of producing more than 5000 pills an hour were confiscated.
Two men in Auckland have been charged with offering to supply the drug 4-MEC. Another man was to appear in Hamilton District Court on Thursday on charges of importing, selling and possession for supply.
Police say more arrests are expected.