River Phoenix died of an acute, combined drug intoxication outside the Viper Room in West Hollywood on the early hours of October 31, 1993. The Los Angeles County Coroner later determined the cause of death to be a lethal mixture of cocaine and morphine (the latter reflecting heroin that had been metabolized), along with smaller amounts of other substances such as Valium, marijuana, and ephedrine. The death was ruled accidental.

If you’d like, I can pull more sources or provide a concise timeline of the final hours and the immediate aftermath.