The findings were dramatic:
For each additional year of opiate substitution treatment the hazard of death before long term cessation fell 13% (95% confidence interval 17% to 9%) after adjustment for HIV, sex, calendar period, age at first injection, and history of prison and overdose.
This is a massive effect. Just one year of treatment is competitive with interventions that we would not even think twice about: many drug treatments for cardiovascular disease fall into this range. Since we can't really randomize people to these types of treatments, the prospective cohort design is likely as good as it gets. So perhaps these types of dramatic findings, if properly replicated, can start a discussion about harm reduction once the behavior is initiated. After all, there is a large population of injectable drug users and finding ways to improve their (fairly poor) outcomes seems like a decent way to improve public health.