SAN FRANCISCO — Robin Williams’ autopsy found no alcohol or illegal drugs were in his body when he killed himself at his Northern California home in August, sheriff’s officials said Friday.

The results released by the Marin County sheriff’s office found that the actor had taken prescription medications, but in “therapeutic concentrations.”

The coroner ruled Williams’ death a suicide that resulted from asphyxia due to hanging.

Sheriff’s officials have said Williams was found in the bedroom of his home in Tiburon on the morning of Aug. 11. His death had been preliminarily ruled a suicide, with sheriff’s officials saying he hanged himself with a belt.

Williams’ wife, Susan Schneider, has said the actor and comedian was struggling with depression, anxiety and a recent Parkinson’s diagnosis when his personal assistant found him dead.

Williams had publicly acknowledged periodic struggles with substance abuse, and he had entered a substance abuse program shortly before his death. According to the coroner’s report, his wife told an investigator Williams did not go there because of recent drug or alcohol abuse, but rather to reaffirm the principles of his rehabilitation.

According to his wife, Williams was having trouble sleeping and had shown increased signs of paranoia before he committed suicide, the autopsy report said. Medical records confirmed he was diagnosed with Parkinson’s disease in November 2013 but had symptoms since 2011, including a left arm tremor and the slowing of left hand movements. Treatments with drugs in May 2014 led to some improvement, according to the report, and he remained physically active until his death.

Williams had two types of antidepressants in his system when he died, as well as a Parkinson’s medication, caffeine and another ingredient found in tea and cocoa, the autopsy found.

Authorities have said Williams was last seen alive by his wife when she went to bed the night of Aug. 10. She woke up the next morning and left, thinking he was still asleep elsewhere in the house.

Shortly after that, Williams’ assistant came to the home and became concerned when he failed to respond to knocks at a door. The assistant found the 63-year-old actor in a bedroom, according to sheriff’s officials.

Williams also had superficial cuts on his wrist, and a pocketknife was found nearby.