Substance misuse in patients who have comorbid chronic pain in a clinical population receiving methadone maintenance therapy for the treatment of opioid dependence

Aims: To compare specific substance misuse in treatment-seeking, opioiddependent patients with and without comorbid chronic pain, and to assess the respective value of urinalysis and patient reports in assessing substance misuse.
Methods: Participants comprised a clinical population in a regional NHS Substance Misuse Service in the East of Scotland (N=521). The Brief Pain Inventory - Short Form was used to assess pain and the Maudsley Addiction Profile and urinalysis were used to assess substance misuse at study inception. Urinalysis was used to assess substance misuse during the 5-year followup period. Data were hosted, linked, anonymised and analysed within a national Safe Haven.
Results: Compared with opioid-dependent patients with no pain, a significantly higher proportion of treatment-seeking, opioid-dependent patients with chronic pain were engaged in non-medical benzodiazepine use (69% versus 58%; p=0.016) and illicit cannabinoid use (84% versus 65%; p=0.025) at study inception. Furthermore, a significantly higher proportion of this group was shown to continue non-medical benzodiazepine use (70% versus 42%; p=0.037) and illicit cannabinoid use (100% versus 32%; p=0.002) during the 5-year follow-up period. There were significant correlations between drug screen results and patient-reported use of opioids (Tetrachoric ϱ=0.4944; p<0.001), benzodiazepines (Tetrachoric ϱ=0.2641; p=0.001) and cannabinoids (Tetrachoric ϱ=0.8384; p<0.001).
Conclusions: Whilst gaining control of illicit opioid use during treatment, opioiddependent patients with comorbid chronic pain demonstrated persistent problematic use of benzodiazepines and cannabinoids. This pattern of misuse was shown to persist during the 5-year follow-up period.