This study follows up patients who receive standard treatment for prescription narcotic drug use disorder, including opioids, benzodiazepines, and benzodiazepine-like drugs (z-drugs), at a specialized addiction service. The overall goal is to evaluate the proportion of patients who reduce or cease using prescription narcotics and the factors associated with treatment outcomes. No new treatments will be tested. Instead, the results will be used as the basis for a future randomized controlled trial to optimize treatment for narcotic drug use disorder.

Background: The study covers prescription narcotics and focuses on opioids and benzodiazepines (and related compounds). The use of opioids and benzodiazepines is relatively safe in the short term. However, long-term use for anxiety and chronic non cancer pain has limited scientific support. Moreover, use of opioids and benzodiazepines has been associated with a variety of adverse effects and both opioids and benzodiazepines are highly addictive.

Clinical guidelines advise that narcotic analgesics and sedatives should not be used as first-choice treatments for pain, anxiety, or insomnia. Instead, guidelines recommend psychotherapy, physiotherapy, and non-narcotic pharmacological drugs (such as non-steroidal anti-inflammatory drugs and antidepressants), alternatives that are less addictive and more beneficial over time. Despite such recommendations, benzodiazepines and opioids are commonly prescribed and used over the long term.

For patients who seek treatment for narcotic drug use disorder, tapering by gradual dose reduction is an important component but its effect is not well studied.

Aims: This study aims to investigate the clinical trajectory and treatment outcome among patients with narcotic drug use disorder at specialized addiction treatment services.

Specific aims:

1) The outcome of tapering of narcotic drugs at 6, 12, and 24 months follow-up 2) How the treatments provided (e.g., tapering; tapering plus psychological treatment) are associated with patient outcomes 3) How psychiatric symptoms and comorbidity are associated with patient outcomes 4) Predictors of narcotic drug abstinence and retention in treatment 5) The validity of psychiatric diagnoses in relation to drug use (i.e., whether the diagnosis changes significantly following drug detoxification)

Methods: This is a naturalistic, prospective study of outcomes following treatment at a specialized service for prescription narcotic drug use disorder. Standardized screening and assessment tools will be used to investigate patients at baseline, evaluate the treatment patients receive over a 24-month period, and evaluate patient outcomes.

All patients starting a new treatment period at the center will be invited to participate at the first visit to the clinic or as soon as possible thereafter. Written informed consent will be obtained. The study will conform to Good Clinical Practice (ICH-GCP) and the principles outlined in the Declaration of Helsinki.

Measurements in the study include: urine drug screening, blood chemistry including screening for alcohol biomarkers, Drug Use Disorders Identification Test, Alcohol Use Disorders Identification Test, Patient Health Questionnaire, EuroQol -5D, Clinical Global Impressions Scale, Adult ADHD Self-Rating Scale - Screening, The Mini International Neuropsychiatric Interview, Version 7, the Life Events Checklist, the Insomnia Severity Index, the Benzodiazepine Withdrawal Symptom Questionnaire, the Subjective Opioid Withdrawal Scale, Generalized Anxiety Disorder - 7, Numeric Rating Scale for Pain, PROMIS Pain Interference - Short Form 4a, patient satisfaction, Substance use questionnaire, and Structural Clinical Interview for DSM-IV Axis II Personality Disorders Screening.

Information regarding treatment at the unit (e.g. number and type of visits, somatic or psychiatric diagnoses) will be collected from medical records using the ICD codes. Diagnostic assessment will be performed according to both ICD-10 and DSM-5.

The protocol allows for a 10-year follow-up using national registries.

Study procedures and data collection will be regularly monitored by an external quality assurance organization.

Analyses will be conducted using statistical software; p values < 0.05 will be considered significant. Prescription drug use, retention in treatment and the percentage of participants with negative urine samples and self-reported abstinence will be calculated at follow-ups. Regression analyses will be computed to assess factors associated with the outcome of tapering.

To find a 95 % confidence interval around the point estimate (drug abstinence) with a margin of error not exceeding +/- 5 percentage points, where the assumed proportion is 0.3, at least 322 patients must be included. Alternatively, to find a 95 % confidence interval with a margin of error not exceeding +/- 10 percentage points, at least 81 patients must be included. A minimum of 81 patients will be included in the study. The study will include an analysis of dropout.

Inclusion Criteria:

• Patients seeking treatment for prescription narcotic drug use disorder (ICD-10: F111, F112, F131, and F132)
• ≥ 18 years
• Willing to participate and who have provided written informed consent.

Exclusion Criteria:

• Inability to understand spoken and written study information.
• Having started tapering prior to the start of the study.

Patients starting a new treatment period for prescription narcotic drug use disorder