A powerful prescription painkiller twice as powerful as morphine is circulating on Wanganui's illicit drug market.
But efforts to restrict prescriptions of the drug have brought local script rates down.
Oxycodone, also known as "hillbilly heroin", is a synthetic opiate often prescribed for pain relief associated with fractures, arthritis and cancer.
It is as addictive as morphine, twice as potent, and more expensive.
The drug is now the number one cause of overdose in the United States, ahead of heroin and cocaine.
According to the Best Practice Journal, the use of oxycodone in New Zealand increased by 249 per cent between 2008-2012. It has been subsidised by Pharmac since 2005.
Figures released by the Ministry of Health showed 3253 prescriptions were written in Wanganui for oxycodone in the 2013 financial year, down from 4147 the previous year.
Wanganui District Health Board mental health clinical director Frank Rawlinson said the painkiller started getting traction about three years ago, when prescription numbers increased "dramatically".
"I suspect that you'll probably find that the drug [companies] were very effective at marketing it and so people were using it without following the proper pathways in using lesser drugs first."
Oxycodone was being sold on to the illicit drug market, where most prescription drugs had a "market value", Mr Rawlinson said.
But increased monitoring and education meant it was being more appropriately prescribed by local doctors.
Seizures of the painkiller by police and customs officials had also dropped over the last three years, he said.
"It will always be an addictive substance and hence it will be sought after, but it's not a real issue for us."
Wanganui medical officer of health Patrick O'Conner said the most common opiate addictions in Wanganui were morphine and methadone.
"We do not hear of a lot of use of oxycodone among people addicted to opiates in Wanganui. I think local prescribers are aware that oxycodone has much the same potential, for good and harm, as other injectable opiates such as morphine and methadone, and they are prescribing it with appropriate caution.
"Perhaps there was a earlier perception that 'oxycodone', which sounds more like the low-strength codeine than high-strength morphine, was a safer alternative to morphine, but there is now a general realisation that this is not the case."
Hawke's Bay physician and chairman of the pharmacy and therapeutics committee James Curtis said while national prescription rates had slowed in the past 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]."