"Our findings that an ambulance was called while the subject was still alive in only 10% of cases, and that a substantial minority of heroin users died alone, strongly suggest that education campaigns should also emphasise that it is safer to inject heroin in the company of others, and important to call for an ambulance early in the event of an overdose. Consideration should also be given to trialling the distribution of the opioid antagonist naloxone to users to reduce mortality from heroin use."

Source

Zador, Deborah, Sunjic, Sandra, and Darke, Shane, "Heroin-related deaths in New South Wales, 1992: toxicological findings and circumstances," The Medical Journal of Australia, 1996; 164 (4): 204-207.