Long-term opioid therapy and mental health comorbidity in patients with chronic pain

Evidence suggests that patients with chronic pain and mental illness are more likely to receive long-term opioid therapy (LTOT) and at higher doses but are also at increased risk of experiencing opioid-related harm. This study investigates LTOT and its relationship to mental illness in the setting of a university-based outpatient pain clinic with liaison psychiatric care.

Retrospective analysis of patients with chronic pain admitted between 2011 and 2015. After a 1-year treatment period, patients with non-opioid treatment, guideline-recommended LTOT, and high-dose LTOT were compared, and multiple regression analysis was performed to identify predictors of higher opioid dosage.

Of 769 patients, 46% received LTOT (opioids for >90 consecutive days), 13% at high dosage (>120 oral morphine milligram equivalents [MME] / day). Two thirds of all patients had mental illness. The prevalence of psychiatric diagnoses and prescription rate of psychotropic medication did not significantly differ between groups. Pain chronicity stages, use of antidepressants, and sex significantly predicted MME/day but explained only a minor part of the variance. The association with antidepressants can be attributed to the prescription of antidepressants for analgesic purposes rather than for treating depression. No association with any other type of psychiatric disorders was observed.

This study shows that mental health comorbidity is highly prevalent but that the prescribed opioid dosage is independent of it in the clinical setting of this study. The concept of liaison psychiatric care might have essentially contributed to the "detachment" of opioid prescription and psychiatric conditions but cannot be isolated from other potentially contributing factors within this single-center observational study.