Background: Opioid maintenance treatment (OMT) is generally considered to reduce mortality in opiate dependents. However, the level of mortality reduction is still uncertain. This study investigates mortality reductions in an "intention-to-treat" perspective including all dropouts. The mortality reducing effects of OMT are examined both within treatment and post-treatment. The study separates overdose and total mortality reductions.
Methods: The study is a prospective cross-registry study with up to 7 years follow-up. All opiate dependents in Norway who applied for OMT (a total of 3789 subjects) were cross-linked with data from the death registry from Statistics Norway. Date and cause of death were crossed with dates for initiation and termination of OMT, and subjects' age and gender. A baseline was established from the waiting list mortality rate. Intention-to-treat was investigated by analysing mortality among the entire population that started OMT.
Results: Mortality in treatment was reduced to RR 0.5 (relative risk) compared with pre-treatment. In the "intention-to-treat" perspective, the mortality risk was reduced to RR 0.6 compared with pre-treatment. The patients who left the treatment programme showed a high-mortality rate, particularly males.
Conclusions: OMT significantly reduces risk of mortality also when examined in an intention-to-treat perspective. Studies that evaluate effects of OMT only in patients retained in treatment tend to overestimate benefits. Levels of overdose mortality will influence the risk reduction. Cross-registry studies as the current one are an important supplement to other observational designs in this field.