Ministry of Health figures showed 2743 prescriptions were written in the Wairarapa for oxycodone in the 2013 financial year, down from 3335 the previous year.
Te Hauora Runanga o Wairarapa clinician Debbie Aporo said while she had not dealt personally with oxycodone addiction, new restrictions on the country's methadone programme might have increased use of the painkiller.
"Methadone clients may be accessing it more ... to top up."
People buying and selling prescription drugs to compensate for street drugs they weren't getting was common, she said.
"People use all kinds of stuff and the mind boggles what people will inject into themselves."
Hawke's Bay physician and chair of the pharmacy and therapeutics committee Dr James Curtis said while national prescription rates had slowed in the last year, the drug was still circulating on the black market.
"More oxycodone is diverted to the illicit market than other opiates. I don't think all people who are addicted to it started on it legitimately, some people have just sourced it from their local [dealer]."
In October 2010, Cromwell man Dale Smitheram died of an accidental overdose after injecting himself with oxycodone.
In August the following year, 44-year-old Vito Vari was found dead at his Nelson home after overdosing on the drug.
Executive director of the New Zealand Drug Foundation Ross Bell said there were two pathways Kiwis developed a dependency on the drug.
"Doctor shopping" involved going from doctor to doctor for prescriptions.
A spike in prescription rates since 2008 could also relate to changes in subsidies, making oxycodone an economic "drug of choice".
However, more education with doctors had seen a drop in the volume of prescriptions written.
"The Ministry of Health does a programme called 'Medicines Control' which is meant to keep track of whether there are doctors who are wildly prescribing a range of medicines ... so there might be a bit more awareness."
