Whenever media stories report a surge of deaths from heroin use, it turns out that more potent heroin has recently arrived in a particular city or town.  For example, a recent L.A. Times headline reads

Black tar moves in, and death follows

and the story goes on to explain that

The death was part of a rash of overdoses, 12 of them fatal, that shook Huntington that fall and winter. All were caused by black-tar heroin, a potent, inexpensive, semi-processed form of the drug that has spread across the United States, driven by the entrepreneurial energy and marketing savvy of immigrants from a tiny farming county in Mexico.

These deaths are due to prohibition.  In a legal market, information about potency would be readily available, so few users would suffer these accidental overdoses.