Northland District Health Board is investigating the region's use of strong painkillers after a national commission found the prescription rate was much higher than some parts of the country.
Northland had the fourth highest rate of strong opioid use in the country after Wairarapa, Nelson-Marlborough and Bay of Plenty.
The figures came from the Health Quality and Safety Commission's Atlas of Healthcare Variation, a new database of health services and outcomes. The doses were dispensed from community pharmacies in 2013, and did not include drugs given in hospitals.
However, nearly half of those given the strong opioids had been treated at a public hospital in the week before.
Strong opioids include methadone, morphine, fentanyl and oxycodone. Commonly used weak opioids include codeine, tramadol and dihydrocodeine.