BACKGROUND: Evidence of harms associated with temazepam gel capsule injecting among injecting drug users in Australia led to its withdrawal from manufacture in Australia. Subsequently, diphenhydramine gel capsule injecting was identified among a subset of ethnic Vietnamese injecting drug users. METHODS: Observational fieldwork around an active street-based illicit drug marketplace together with targeted purposive sampling enabled 66 ethnic Vietnamese injecting drug users to be recruited for in-depth interview. RESULTS: Data revealed that the injection of gel capsules increases exposure to non-viral infections. Analysis of participant interviews show how participants have established their own ways of reducing these harms including thinning the drug solution by jacking regularly during injection. Controversially, femoral vein administration of diphenhydramine-heroin cocktails was also seen as a harm reduction strategy by participants. DISCUSSION: Health education campaigns to address the potentially negative consequences of gel capsule groin injection will not be successful unless health workers and policy makers work with drug users and incorporate local understandings and meanings of risk in health promotion activities.