Objectives: International studies indicate that methadone maintenance treatment (MMT) reduces mortality in patients with opioid use disorder, but mortality remains elevated compared to that of the general population. This study investigated risk factors impacting upon mortality among patients on MMT.

Methods: The study was conducted at an addiction treatment clinic. We utilised a case-control design matching all deaths occurring between February 2005 and February 2012 inclusive with another attendee in terms of age and gender.

Results: There were 80 deaths with median age 35 years (inter quartile range (IQR) 30-41 years). The causes of death were categorised as poisoning (48%), medical (36%) and trauma (16%). The median methadone dose of cases was 70mg (IQR 55-90) and was not significantly different from the control group (median 80mg, IQR60- 90, p=0.58). There was no significant difference between the fatalities and the controls in terms of recent misuse of cocaine. Cases were more likely to have a history of imprisonment (71% versus 35%, p<0.001), HIV infection (29% versus 12%, p=0.01) and non-HIV related medical problems (47% versus 16%, p<0.001). They were also more likely to have missed attendance at the clinic for at least one week (23% versus 1%, p<0.001).

Conclusions: Methadone dose was not associated with increased mortality. A life history of imprisonment (not only recent release) was a marker for increased risk of death while on MMT. Treatment non-attendance was associated with increased mortality and services should seek to actively follow-up on patients who drop out of treatment.