FIGURE.

Causal diagram for the plausible relations between chronic pain, opioid prescriptions, and mortality in the presence of measured and unmeasured confounders. ^aChronic pain (X) was self-reported and defined as reporting to have experienced pain for at least three months. ^bOpioids (M) include codeine, dihydrocodeine, meperidine, pentazocine, propoxyphene, tramadol, hydrocodone, morphine, tapentadol, fentanyl, hydromorphone, methadone, oxycodone, and oxymorphone. ^cMeasured covariates (C): Age, sex, race, education levels, poverty-income ratio, health insurance coverage, marital status, smoking, alcohol intake, and anti-depressant medication prescription. Illicit drug use was additionally adjusted for in a sensitivity analysis because the information was only available for participants aged 20-59 years. In the sensitivity analysis, we additionally adjusted for comorbidities such as cardiovascular diseases, cancer, and arthritis.