Pain, psychological flexibility, and continued substance use in a predominantly hispanic adult sample receiving methadone treatment for opioid use disorder.

Background: We explored pain, psychological flexibility, and continued substance use among 100 adults treated with methadone for opioid use disorder (OUD). All participants had co-occurring chronic pain.

Methods: Participants recruited from a community treatment center between 2009 and 2010 completed an interviewer-facilitated assessment. Chronic pain severity and interference, psychological flexibility (mindfulness, acceptance, values success), past 30-day substance use, and demographics were reported. We modeled a zero-inflated negative binomial regression to examine 1) the probability that an individual does not use illicit substances and 2) illicit substance use frequency among those expected to use. Pain severity and mindfulness were included as predictors in the logit (zero inflated) model. Pain interference, acceptance, and values success were included as predictors in the negative binomial (count) model. We controlled for age and gender in both models.

Results: Participants were predominantly (84%) Hispanic, and 64% used an illicit substance least once in the past 30 days. Greater degree of mindfulness significantly predicted the probability that an individual does not continue to use illicit substances (OR = 1.59, p <  0.05). Lower degree of values success significantly predicted greater illicit substance use frequency among those likely to use (IRR = 0.72, p < 0.01). No other variables were associated with continued substance use.

Conclusions: Findings suggest psychological flexibility is associated with continued substance use in this predominantly Hispanic sample of adults treated for OUD with co-occurring chronic pain. Study findings may have implications for how to address the treatment needs of this complex population.