Background Opioid use disorder is best conceptualized as a chronic relapsing illness which, though associated with elevated rates of morbidity and mortality, has the potential to be in sustained long-term remission with appropriate treatment. Opioid use disorder may involve the use of illicitly manufactured opioids, such as heroin or street fentanyl, or pharmaceutical opioid medications obtained illicitly or used non-medically. While current Canadian estimates are lacking, opioid use disorder is estimated to affect approximately 2.1% of Americans.1
The state of public health emergency declared in 2016 in response to the sharp increase in overdose deaths in British Columbia underscores the importance of developing a coordinated evidence-based strategy to address untreated opioid use disorder and related harms. The recent emergence of street fentanyl, a highly potent synthetic opioid increasingly used to replace or dilute (or "cut") heroin and other illicit opioids, is a pressing public health concern that has contributed significantly to the overdose crisis. Provincial surveillance data indicate that the proportion of illicit drug overdose deaths involving fentanyl has rapidly increased from 5% in 2012 to approximately 30% in 2015. 2 From January 1 to July 31 2016, there were 264 overdose deaths where fentanyl was detected, representing 60% of all overdose deaths reported. This is a 222% increase in overdose deaths involving fentanyl compared to the corresponding time period in 2015 (82 deaths). A key component of an evidence-based provincial response is the delivery of health services that optimize engagement, care and treatment of individuals with opioid use disorder, and recognize the need for a diversity of available treatment options that can be matched to individual patient needs and circumstances.
For many years, methadone has been the most commonly prescribed pharmacotherapy for the clinical management of opioid use disorder, and British Columbia has long benefited from a methadone maintenance program stewarded by the College of Physicians and Surgeons of British Columbia (CPSBC). 3,4 However, recent reports have highlighted the low number of methadone prescribers in British Columbia, particularly in Northern regions, as well as poor retention rates. 5 In addition, a number of additional treatment options have been under-utilized, and evidence-based reviews have increasingly described the benefits, side-effect profiles and safety of these various approaches to treatment of opioid use disorder. This literature, which is reviewed in detail below, enables the development of treatment strategies for opioid use disorder that employ different approaches based on the comparative safety profile of different treatments, individual patient circumstances and comorbidities, and recognize that treatment can be intensified or simplified depending on patient circumstances as well as short-and long-term response to treatment.

# Scope and Purpose
The objective of this guideline is to provide recommendations, supported by current and rigorously reviewed evidence, for the full spectrum of medical and psychosocial interventions available to treat opioid use disorder.
In doing so, the guideline aims to provide comprehensive education and clinical care guidance to health care providers spanning the addiction care continuum in the province, which will, in turn, improve access to evidence-based treatment for patients and families, and reduce the significant harms associated with opioid use disorder in British Columbia.
Although the evidence presented here is generally extrapolated from studies conducted in adult populations, the consensus of the committee is that many of these recommendations are equally relevant and applicable to adolescent (aged 12-17 years) and young adult (aged 18-25 years) populations. More specifically, and in line with CPSBC recommendations and a recent policy statement from the American Academy of Pediatrics, 6,7 the committee recommends that any clinician providing care to adolescents and young adults with moderate to severe opioid use disorders should consider offering first-line pharmacotherapy options where indicated and appropriate. If administration of pharmacotherapy to this patient population is beyond scope of practice or expertise, care providers should refer such patients to a health care professional with experience in treatment of adolescents and young adults with substance use disorders.
While this guideline reviews research evidence regarding treatment of opioid use disorder in the general population, future work is required to develop and implement best practices in specific populations, including adolescents and young adults, the elderly, pregnant women, and Indigenous populations (e.g., culturally optimized care pathways), as well as within criminal justice and correctional settings. Additionally, the development of best practices for managing mild concurrent mental health issues in the context of opioid addiction is required. Importantly, clinicians should be aware that treatment options may be limited for individuals subject to provincial or federal workplace-related legislation (e.g., health care professionals), but that these individuals may be eligible for alternative treatment programs (e.g., antagonist medications, and/or non-agonist based residential or psychosocial treatments). In addition, opioid agonist prescribers should be aware that some individuals (e.g., those in safety sensitive positions) may require modification of workplace duties if on opioid agonist therapy and should be aware of the obligation to work with patients and to consult with regulatory bodies and others (e.g., CPSBC, Canadian Medical Protective Association) regarding obligation to notify employers in these circumstances. Best practices for the treatment of opioid use disorder in this context also need to be better defined.
Finally, while primary prevention and the importance of safe prescribing of prescription opioids to prevent misuse and addiction are outside the scope of this guideline, it is acknowledged that for individuals who have developed a physiological dependence to prescription opioids but not opioid addiction, a slow, clinically-supported tapered reduction in prescribed dosage may be most appropriate strategy. If recognized and addressed early, individuals with physiological dependence have the potential to safely undergo a slow tapered dose reduction in an outpatient or primary care setting using non-pharmacotherapeutic approaches. In the long-term, monitoring, early intervention, and primary care management of prescription opioid dependence may reduce or prevent health care expenditures and long-term health care involvement associated with opioid use disorder. Readers are encouraged to consult the College of Physicians and Surgeons of British Columbia Professional Standards and Guidelines for Safe Prescribing of Drugs with Potential for Misuse/Diversion for more information on safer prescription opioid prescribing strategies at www.cpsbc.ca/files/pdf/PSG-Safe-Prescribing.pdf.

# Intended Audience
The guideline is intended to be used by physicians, nursing and allied healthcare professionals with and without specialized training in addiction medicine. In addition, this guideline is intended to be a resource for policy makers and healthcare administrators in the development of strategies and programs to best address unmet addiction care needs within British Columbia in an evidence-based, cost-effective manner.

# Funding and Committee Membership
Guideline development activities were entirely supported by internal funding from the BC Centre on Substance Use (BCCSU), without support from the pharmaceutical industry or associated stakeholders.
Through funding provided by the British Columbia Ministry of Health in 2014 and the work of the BCCSU's Inaugural Governance Board, a strategy to prepare a provincial guideline for the treatment of opioid addiction was initially established in the spring of 2015. Subsequently, in the summer of 2016, in consultation with the provincial government's Joint Task Force on Overdose Response and advisors from the Ministry of Health, three to five candidates were invited from each regional Health Authority and the First Nations Health Authority, as well as representatives from BC Corrections Services and the Ministry of Health, to form a provincial guideline committee. Ultimately, an interdisciplinary committee of 28 individuals was assembled. Consistent with best practice for guideline development, the BCCSU used the AGREE-II instrument8 throughout the development and revision phases to ensure the guideline met international standards for transparency, high quality and methodological rigour.