Data on sociodemographic and clinical characteristics came from claims records in the 12-month period prior to the index date of the opioid use episode. The Charlson comorbidity index10 was used as a measure of overall medical comorbidity. In addition, we also collected information on International Classification of Diseases, Ninth Revision, Clinical Modification (ICD-9-CM) pain diagnoses in the 12 months before the index date. Arthritis and/or joint pain, back pain, neck pain, and headache were selected as tracer pain diagnoses to be tracked individually because these were the most commonly reported pain sites in the World Health Organization Collaborative Study of Psychological Problems in General Health Care.11 We also collected information on the presence of the following other (nontracer) pain diagnoses: extremity pain, abdominal pain, chest pain, kidney stones and/or gallstones, pelvic pain, rheumatoid arthritis, fractures, neuropathic pain, fibromyalgia, and temporomandibular joint pain. These conditions were summed to create the number of nontracer pain diagnoses. Mental health and substance use disorders were classified into the following groups based on ICD-9-CM diagnoses using validated grouping software developed by the Agency for Healthcare Research and Quality (Clinical Classifications Software [CCS], 2008 release; Agency for Healthcare Research and Quality, Rockville, Maryland): adjustment disorders, anxiety disorders, mood disorders, personality disorders, and substance use disorders. Mood disorders were further classified as unipolar depressive disorder or bipolar disorder; substance use disorders were further classified as alcohol-use disorder, nonopioid-use disorder, or opioid-use disorder. Adjustment, anxiety, mood, and personality disorders were also summed to create a variable identifying the number of mental health disorder types.