A Sydney doctor who has delivered seminars on drug dependency has been struck off the register of medical practitioners for prescribing addictive painkillers to patients who were hooked on their medication.

Dundas Valley GP Kelvin Lo inappropriately prescribed opioids and powerful anxiety medication to 14 patients, in some cases when he knew or should have known that they were likely to be abused

The Health Care Complaints Commission cancelled Dr Lo's registration after finding that he had engaged in professional misconduct.

He prescribed one patient 2375 tablets of the insomnia drug Nitrazepam over a period of 13 years, despite admitting under cross-examination that the medication should only be used for two to four weeks.

He prescribed another woman an "excessive" quantity of the painkiller pethidine, which an expert witness told the HCCC had not been prescribed for a recognised therapeutic purpose.

Dr Lo, who was registered under the name Kwong Yiu Lo, said he was not feeding the woman's habit but motivated by a desire to help her.

But expert witness Harry Nespolon said it was clear that the patient had an addictive personality and was abusing her medication, with obvious signs such as "losing" her prescriptions and seeing multiple doctors.

Dr Lo admitted that another patient, who he prescribed the anxiety drug Alprazolam without performing a proper medical assessment, was a drug-seeking patient who had "hoodwinked" him and his colleagues.

He told the commission it was unclear how to define a drug-dependent patient, but conceded under cross-examination that he had been to lectures where this was discussed and delivered lectures on drug dependency.

In a decision published on Tuesday, the HCCC banned Dr Lo for reapplying for registration for two years, finding that he did not possess insight into the gravity of his conduct.

"The respondent's conduct was reckless and showed a blatant disregard of the law," the HCCC found. "We are concerned by the respondent's failure properly and lawfully to prescribe drugs of addiction.

"This failure has the potential to allow their entry into the community where they could become available to drug abusers, thus raising a serious issue of protection of public health and safety."

The use of opioids for pain management has quadrupled in Australia over the past decade.

The opium-derived drugs, which act on the central nervous system to reduce pain, caused 564 accidental deaths in 2012.

A report on healthcare variations found some parts of Australia were dispensing opioids at a rate 10 times higher in some areas than others, possibly due to poor prescribing practices by GPs.

Pain Australia chief executive Lesley Brydon said the willingness of some GPs to prescribe opioids over a long period of time reflected the long waiting times and little awareness of multidisciplinary clinics to manage chronic pain.

"Opioids are not suitable for long-term use," Ms Brydon said.

"They're incredibly valuable in the management of acute pain but for long-term use they're not suitable and, what's more, they're shown not to be effective."

Medical groups have called on the federal government to introduce a real-time monitoring system for opioid prescriptions, which would alert doctors and pharmacists to patients who were doctor shopping for new prescriptions.