The report said the coroner found cocaine, alcohol and the powerful opioid fentanyl in Miller's system and his death has been ruled as "accident".
The rapper, whose real name was Malcolm James McCormick, was found unresponsive in his home in the Studio City neighbourhood on September 7.
Miller had long suffered from substance abuse and was even vocal about it.
In his deeply personal 2014 mixtape "Faces", the rapper had addressed his drug addiction.
The pair, who met in 2012, collaborated on a number of songs and performed together at the One Love Manchester concert in 2017.
Miller became popular at the age of 18 with his mixtape 'K.I.D.S.' in 2010. His best-known songs include "Loud", "Smile Back", and a collaboration with Grande called "The Way".
His most commercially successful album was 2011's 'Blue Side Park'.
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