Heroin is often the next step when prescription narcotic painkillers become too expensive, and harder to obtain. Heroin is cheaper. easier to procure, and stronger these days.
The basic problem with overdosing on heroin is dosage control. There is none. You don't know how potent the drug is, what it is cut with, and other variables that blow in the wind when buying street drugs like this. And those that abuse this drug often do so in combination with either alcohol, and/or tranquilizers, ramping up the chance for overdosing, and death.
