Robin Williams had no alcohol or illegal drugs in his system when he committed suicide, a post-mortem examination has found.

The Oscar-winning actor took his life at his Northern California home three months ago. He was found in the bedroom of his home on the morning of 11 August.

The Marin County sheriff's office released the autopsy results on Friday (7 November), ruling the death a suicide resulting from asphyxia by hanging.

The actor had taken prescription medications, but in "therapeutic concentrations", said the coroner.

The 63-year-old was reportedly suffering severe depression and waged a public battle with addiction for many years. He had recently entered a 12-step rehab programme for drug abuse.

It was later suggested that Williams may have committed suicide after being diagnosed with Parkinson's disease.

Friends of the comic actor said that he feared the disease may have stopped him cycling, a sport he took up to battle his drink and drugs addiction.

Following his death, his grief-stricken wife Susan Schneider said in a statement: "I am utterly heartbroken ... As he is remembered, it is our hope the focus will not be on Robin's death, but on the countless moments of joy and laughter he gave to millions."

As all of Hollywood honoured the much-loved star, President Barack Obama led the tributes to the American funny man, describing him as "one of a kind."

Williams won an Oscar (best supporting actor) for Good Will Hunting in 1998 and Golden Globe awards for his performance in movies Mrs Doubtfire, Good Morning Vietnam and The Fisher King.