Phillip Seymour Hoffman died of acute drug overdose, with a mix of heroin, cocaine, benzodiazepines, and amphetamines found in his blood. The 46-year-old-actor, who had spent years in recovery helping others, was also found with a large quantity of what was believed to be heroin. His overdose, which was ruled an accident, likely resulting from tolerance. Hoffman’s drug “cocktail” is a process known as stacking, which some people use to increase effects of substances as tolerance grows. However, it also often influences breathing and causes respiratory depression, resulting in death.