http://www.usatoday.com/news/health/2006-05-04-heroin-mix_x.htm
"Unusually potent heroin laced with a powerful painkiller has killed more than two-dozen people and sent more than 300 to hospitals across the eastern USA during the past three weeks, local and federal officials say. The culprit in many of the cases appears to be heroin mixed with fentanyl, a potent form of synthetic morphine that is used to treat extreme pain. Veterinarians use one formulation of it to immobilize large animals. The mixing of such a powerful, costly drug with heroin for street sales is very unusual."
