Robin Williams had no alcohol or illegal drugs in his system when he took his life at his Northern California home three months ago, a post-mortem examination has found.

The Marin County sheriff’s office released the autopsy results on Friday, ruling the death a suicide resulting from asphyxia by hanging.

“Toxicological evaluation revealed the absence of alcohol or illicit drugs,” said a brief statement.

The Oscar-winning actor had taken prescription medications, but in “therapeutic concentrations”, it added.

The 63-year-old star of Good Will Hunting, Good Morning, Vietnam and Mrs Doubtfire was found dead by his personal assistant in the bedroom of his home on the morning of 11 August.

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A few days after his death, Williams’ wife Susan Schneider said her husband had been suffering from depression and the early stages of Parkinson’s disease.

She saw him alive before she went to bed on the eve of his death.

Ms Schneider was probably at home at the time the actor killed himself, the sheriff’s office has said.

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The father-of-three had joked in the past about his battles with alcoholism and drug abuse.

He had entered a substance abuse rehabilitation programme shortly before his death.

The actor’s ashes were scattered in San Francisco Bay, according to media reports.

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