People with chronic heroin addiction may soon have another treatment option after the conclusion of a groundbreaking study in Vancouver's Downtown Eastside.

The four-year Study to Assess Longer-term Opioid Medication Effectiveness (SALOME), led by principal investigator Dr. Eugenia Oviedo-Joekes, examined whether hydromorphone, a licensed pain medication, is as effective in treating a chronic heroin addiction as diacetylmorphine, also known as pharmaceutical-grade heroin.

The results, which will appear in Wednesday's edition of the Journal of the American Medical Association Psychiatry, show it is: Participants on both medications reported three to five days a month of illicit drug use, compared with almost daily illicit drug use prior to the study. As well, illegal activities dropped to an average of less than four a month, compared with an average of more than 14 a month before the study.

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Participants in the double-blind study could not determine which drug they were receiving, researchers found.

It's the first time hydromorphone, commonly used in palliative and acute care, has ever been evaluated as a substitution treatment for opioid dependence.

"Chronic addiction has huge consequences for individuals and society," said Dr. Scott MacDonald, who oversaw trials at Providence Health Care's Crosstown Clinic from late 2011 to late 2015. "We now have an additional treatment option – one that does not have the political and regulatory obstacles and stigma that prescription heroin has to it."

Hydromorphone is also readily available in Canada, whereas prescription heroin is manufactured by a pharmaceutical company in Europe and must be imported through an onerous process.

This new option builds on heroin-assisted treatment, a secondary treatment targeted at entrenched addicts who have failed repeatedly with traditional options such as methadone or buprenorphine. For them, receiving prescription-grade heroin in a supervised, medical setting has been shown to improve physical- and mental-health outcomes and reduce illicit drug use and related criminal activity.

SALOME's 202 participants averaged more than 15 years injecting street heroin and had attempted methadone several times in the five years prior to beginning the study.

Dr. Oviedo-Joekes, SALOME's lead researcher, noted that 80 per cent of participants stuck with the study – an important finding, because injection drug users are at high risk for HIV and other blood-borne illnesses and may not frequently engage with the health-care system. During the study, participants saw doctors three times a day.

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"We see them every day. We have an opportunity to provide comprehensive care," she said. "This is a very small group of patients – not more than 10 per cent of everybody on substitution treatment – but they are the ones that are the most vulnerable. They are the ones we have failed over and over with every other treatment."

No one from the College of Physicians and Surgeons of B.C. was available to comment on the research on Tuesday. In an e-mailed statement, the college said its Prescription Review Program staff "will be interested in reading the full study to understand the implications going forward."

SALOME is the next chapter of the North American Opiate Medication Initiative (NAOMI), North America's first clinical trial of prescription heroin, which took place from 2005 to 2008. That study confirmed the effectiveness of heroin-assisted treatment – currently offered in countries including Switzerland, Denmark, Germany, the Netherlands and the U.K. – but produced the unexpected finding that a small group of participants that had received hydromorphone seemed to yield the same benefits.

SALOME was then launched to investigate whether hydromorphone is as effective as prescription heroin in heroin-assisted treatment.

The trials drew the ire of Conservative former federal health minister Rona Ambrose, who objected to Health Canada's approval of special applications allowing people cycling out of the study to continue receiving prescription heroin. In October, 2013, Ms. Ambrose introduced regulations to make prescribing the drug outside of a clinical trial illegal.

Providence and five plaintiffs launched a constitutional challenge and sought an injunction while the case was before the courts; the B.C. Supreme Court sided with them the following May, saying the risks associated with severe heroin addiction "will be reduced if [the addicts] receive injectable diacetylmorphine treatment from Providence physicians."

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Crosstown Clinic currently treats upward of 140 people per day. Currently, 110 are on prescription heroin, about 25 are on injectable hydromorphone and a "small number" are on oral hydromorphone, Dr. MacDonald said.