Payne, 31, who shot to global fame with the boy band, was found dead after he fell from a third-floor hotel room balcony in Buenos Aires on Wednesday, triggering an outpouring of fan tributes.
In the first official details of the autopsy, the prosecutors office said coroners had found 25 injuries compatible with those caused by a fall from height, including fatal head injuries, with internal and external bleeding.
It added that there were no signs of a third party being involved, though the incident was being investigated as a "suspicious death" out of protocol.
"Everything indicates that the musician was alone when the fall occurred, and was going through some kind of episode due to substance abuse," the prosecutors office said.
"City police who surveyed the scene found substances inside the room that at first glance - and pending confirmation from the experts - would be narcotics and alcoholic beverages, as well as several destroyed objects and furniture," it added.
Police earlier said in a statement they had found the room in "total disorder" in a search after his death, with various things smashed and medications scattered around.
While details surrounding his death remain unclear, Payne had spoken publicly about his struggles with mental health and using alcohol to cope with the pressures of fame.
WHISKEY, ANXIETY MEDICATION
The city police said that in the atrium of the hotel where Payne had fallen they had found a bottle of whiskey, a lighter and a cellphone. They said they had collected fingerprints from those.
In the room of the luxury hotel in the city's trendy Palermo district, police said they found over-the-counter medications, energy packs and anxiety drug Clonazepam.
"Upon entering, total disorder was observed, with various elements broken," the police said in a statement, adding they had taken more fingerprints and other evidence to be analyzed in labs, as well as a notebook and passport.
"The balcony area was inspected in order to establish access to it," the police force added.
Before Payne's fall, a hotel employee had called emergency services, asking for help with a guest who was trashing his room and appeared to be under the influence of drugs or alcohol, audio obtained from the Buenos Aires security ministry showed.
"We have a guest who is intoxicated by drugs and alcohol. And, well, he's ... When he's conscious, he breaks, he's breaking the whole room. And, well, we need you to send someone, please," the hotel worker told police in the 911 call.
"We need you to send someone urgently because, well, I don't know if the guest's life is at risk. He is in a room with a balcony. And, well, we are a little afraid that he will do something that will put his life at risk."
One Direction found global success after Simon Cowell brought together Payne, Harry Styles, Zayn Malik, Niall Horan and Louis Tomlinson on Britain's X Factor talent show in 2010.
They went on to sell 70 million records, with six top-10 hits on Billboard's Hot 100, including "What Makes You Beautiful", "Story of My Life" and "Live While We're Young". Payne's co-writing credits included "Story of My Life" and "Night Changes".
