BACKGROUND The extent of suicide among addicts in the UK has not been sufficiently examined. OBJECTIVE To examine suicide trends among registered addicts in the UK over a 25-year period. METHODS We quantified suicide using International Classification of Diseases (ICD) external death codes E950-959, calculated annual age-standardised suicide rates, standardised mortality ratios (SMRs) and described trends in methods of suicide and drug overdose suicides in five successive cohorts of registered addicts. RESULTS Male and female suicide rates are 69.0 and 44.8 per 100,000 person-years, respectively. There was a consistent decline in suicide rate throughout the 25-year period. Among males, the SMR for suicide declined from 17.2 in 1968-1972 to 4.4 in 1988-1992 (SMR ratio = 3.9, 95% CI = 2.5-6.1); among females it declined from 52.6 to 11.3 in the same period (SMR ratio = 4.7, 95% CI = 1.9-10.8). Drug overdose was the most common method of suicide, accounting for 45% of cases. Significant increase in antidepressant (percentage difference = 23.5%, 95% CI = 15.2-31.8) and methadone (percentage difference = 11.0%, 95% CI = 0.5, 21.5) overdose in 1988-1992 compared with 1968-1972 was reported. CONCLUSIONS The findings confirm that addicts are still at higher risk of suicide than the general population and that prescribed drugs, notably antidepressants and methadone, influence this heightened risk.