Longitudinal analysis of pain and illicit drug use behaviors in outpatients on methadone maintenance

Background: Little is known about the experience of chronic pain and the occurrence of illicit drug use behaviors in the population enrolled in methadone maintenance treatment (MMT) programs. Methods: This is a secondary analysis of longitudinal data from two MMT samples enrolled in a randomized controlled trial of hepatitis care coordination. Patients completed pain, illicit drug use, and other questionnaires at baseline and 3, 9, and 12 months later. Associations were sought over time between the presence or absence of clinically significant pain (average daily pain ≥4 or mean pain interference ≥4 during the past week) and current illicit drug use (i.e., non-therapeutic opioid, cocaine or amphetamine use identified from self-report or urine drug screening). Results: Of 404 patients providing complete data, within-patient variability in pain and illicit drug use was high across the four assessment periods. While 263 denied pain at baseline, 118 (44.9%) later experienced clinically significant pain during ≥1 follow-up assessments. Of 180 patients (44.6%) without evidence of illicit drug use at baseline, only 109 (27.0%) had similar negative drug use at all follow-up assessments. Across four assessment periods, there was no significant association between pain group status and current illicit drug use. Conclusions: This one-year longitudinal analysis did not identify a significant association between pain and illicit drug use in MMT populations. This finding conflicts with some earlier investigations and underscores the need for additional studies to clarify the complex association between pain and substance use disorders in patients in MMT program settings.