Aims It has been suggested that starting and temporarily discontinuing methadone treatment is related to an increased risk in overdose mortality. This study describes the incidence of overdose mortality in relation to time after (re)entering or leaving treatment.
Design A dynamic cohort of 5200 Amsterdam methadone clients was observed during treatment and (a maximum of 1 year) after treatment.
Findings Between 1986 and 1998, 29 729 person-years (py) and 68 overdose deaths were recorded, leading to an overdose mortality rate of 2.3/1000 py (2.2 during and 2.4 after treatment). A modest increase was observed during the first 2 weeks after (re)entering treatment; 6.0/1000 py (rate ratio: 2.9; 95% confidence interval 1.4; 5.8). Directly after leaving treatment no increase was observed.
Conclusions Inhaling heroin, common among Amsterdam heroin users, is thought to account for low OD mortality rates both during and after treatment. Accumulation of methadone, inadequate assessment of tolerance of known clients re-entering treatment and concurrent periods of stress or extreme heroin use when entering treatment are mentioned as possible explanations of the increased risk within the first 2 weeks. An Australian study reported a much higher increase. The modest increase in Amsterdam is explained by low background risk of overdose mortality, low starting dosage and the low threshold to treatment.