Hoffman died from a mix of heroin, cocaine, amphetamines and benzodiazepines, which are psychoactive drugs, said a spokeswoman for the New York City medical examiner. The death was ruled an accident.
Law enforcement officials have said Hoffman was found Feb. 2 with a needle in his arm, and tests found heroin in samples from at least 50 packets in his Manhattan apartment.
Police had been investigating his death as a suspected drug overdose. An autopsy in February was inconclusive and medical examiners said more tests were needed.
Authorities also found unused syringes, a charred spoon and various prescription medications, including a drug used to treat heroin addiction, a blood-pressure medication and a muscle relaxant.
Detectives discovered two diaries but they did not include suicidal thoughts or chronicles of drug activity, ABC News reports, but they did contain musings about his struggle with addiction, as well as thoughts that were tough to decipher.
Hoffman, 46, who won an Oscar for "Capote" and starred in numerous other movies as well as New York stage productions, had been frank about struggling with substance abuse. He told CBS' "60 Minutes" in 2006 that had he used "anything I could get my hands on" before getting clean at age 22. But in interviews last year, he said he'd relapsed, had developed a heroin problem and had gone to rehab for a time.
Investigators have been probing how Hoffman may have obtained the heroin. Tests of the heroin in his apartment have found that it was not cut with a dangerous additive such as fentanyl, a synthetic form of morphine used to intensify the high that has been linked to deaths in other states.
A musician, veteran jazz player Robert Vineberg, has been charged with keeping a heroin stash in a lower Manhattan apartment amid the investigation into Hoffman's death. Vineberg, who has said he was a friend of the Tony Award-nominated Hoffman, hasn't been charged in Hoffman's death and has said he didn't sell him the heroin found in his apartment.
As police followed a tip after Hoffman's death, they said they found about 300 small bags of heroin, worth about $10 apiece on the street, and $1,300 in cash in Vineberg's apartment and music studio.
The Associated Press contributed to this report
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