Aims. To ascertain the prevalence and patterns of antidepressant use among IDU in Sydney and to determine ally harm associated with antidepressant use. Design. Cross-sectional survey. Setting. Sydney, Australia. Participants. Two hundred and one Sydney injecting drug users (IDU) recruited through advertisements, needle exchanges, methadone maintenance clinics and by, word of mouth. Findings. Forty percent of subjects had used antidepressants, 21% in the preceding 6 months. Similar proportions of subjects had used tricyclics (26%) and selective serotonin reuptake inhibitors (SSRIs) (24%), with 8% reponing use of a monoamine oxidase inhibitor. Recent use favoured the SSRIs; however, there was still widespread use Of tricyclics. The injection of antidepressants was rave, with only three subjects reporting Ever having injected the drugs. Antidepressant use was associated with higher levels of polydrug use, poorer health, higher levels of psychiatric distress and a greater risk of heroin overdose. The excess risk of overdose was specifically associated with tricyclics, rather than SSRIs. Conclusions. The study confirmed that, like other pharmaceutical products, the use of antidepressants was common among IDU in Sydney. The prescription of tricyclics to heroin users would appear to increase their risk of overdose. If it is considered appropriate to prescribe antidepressants to IDU, it would appear safer to prescribe SSRIs.