Robin Williams' autopsy has found there were no signs of alcohol or illegal drugs in his body when the actor killed himself at his Northern California home in August.

The autopsy results released by the Marin County sheriff's office has found while Williams had taken prescription medications, these were within what they term "therapeutic concentrations".

The coroner has ruled Williams' death a suicide that resulted from asphyxia.

Williams' wife, Susan Schneider, has said the actor and comedian had been struggling with depression, anxiety and a recent Parkinson's diagnosis.