Characteristics and problematic opioid use in people prescribed opioids for CNCP over four years: a prospective cohort study

Background: The increase in long-term prescribing of opioids for chronic non-cancer pain (CNCP) overseas and in Australia (15-fold increase in opioid prescribing over the past two decades) has been accompanied by increases in problematic opioid use and harms including overdose and dependence. Previous cross-sectional research suggests that problematic use, such as aberrant behaviours and dependence, is associated with increases in pharmaceutical opioid dose. To date, however, there have been limited long-term studies (>12 months). The aim of the current study is to examine the association between pharmaceutical opioid dose in people living with CNCP and associations with problematic use over four years

Method: The Pain and Opioids IN Treatment study is a large, national prospective cohort of 1,500 people prescribed pharmaceutical opioids for CNCP. We utilised data from four waves: baseline, 1-year, 2-year, 3-year and 4-year follow-ups. Over 80% of the baseline cohort completed each wave. Current opioid dose was estimated in oral morphine equivalent (OME) mg. Measures of problematic use include: ICD-10 pharmaceutical opioid dependence and harmful use, assessed using the Composite International Diagnostic Interview. Aberrant behaviours were assessed through the Opioid Related Behaviours In Treatment scale, these included, asking for an early script renewal and asking for an increase in dose. Patient-centred problems and concerns were assessed through the Prescribed Opioids Difficulties Scale. Mixed effects models, using multiple imputation for missing data, adjusted for a number of confounders including age, gender, pain, mental health and a history of substance use.

Results: Current opioid dose varied widely: at baseline, 8.8% were taking <20mg OME per day, 52.1% were taking 21-90mg OME, 24.3% were taking 91-199mg OME and 14.8% were taking >=200mg OME. At the 4-year follow-up 20% of the baseline sample had discontinued their opioid use; 20% were consuming 91-199mg OME per day and 11% were consuming doses >=200mg OME per day. Over the four waves, proportion meeting criteria for ICD-10 dependence ranged from 8.8% to 12.0%, harmful use ranged from 14.3% to 16.5%, engagement in aberrant behaviours ranges from 31.1% to 38.5%. Approximately 2% reported an overdose each year of the study. Two-thirds of the sample consistently scored moderate to high on patient-centred problems and concerns. There was a clear dose response with pharmaceutical opioids use and problematic behaviours, and dose was significantly associated with problematic use in fully adjusted mixed-effects models.

Conclusion: Consumption of higher opioid doses is associated with increased risk of problematic behaviours over 4 years and is more likely among people with a complex profile of physical and mental health problems.