New York Police Lieutenant Gene White said: 'At present, there are no signs of drug use or foul play. There is no drug evidence at the apartment.
'The door was locked from the inside and there were no signs of a struggle.'
But earlier, officers had said they believed the death was drugs-related.
The 46-year- old was the youngest son of Kirk Douglas. He had small parts in films such as The Golden Child and Delta Force III: The Killing Game but gave up acting more than a decade ago to try his hand at comedy and songwriting.
In his private life, he was in and out of rehabilitation clinics and had a criminal record for violent behaviour - which included a 30-day prison sentence for drunkenly attacking an air steward on board a flight.
Douglas's life was the all-too-familiar story of the inadequate product of a high-achieving family who feels he has failed to live up to expectations.
The fact that his half-brother Michael is one of the world's highest paid actors and married to Catherine Zeta- Jones only brought his perceived failings into sharper focus.
He admitted he envied his brother's good fortune in snaring the 'sweet, charming, considerate' Miss Zeta-Jones, and added: 'What I envy more is that he let it happen. He didn't rush into it.'
Friends said Eric was often nervy, agitated and volatile, with his speech fast yet unfocused.
'People think I have it easy because I'm Kirk Douglas's son or Michael Douglas's brother,' he said in an interview with the Daily Mail. 'But the truth is that sometimes it's harder.
'Being related to famous people is something you always have to work on.'
Eric was the second son of Kirk Douglas's second marriage, to publicity agent and producer Anne Buydens. Michael was born to Kirk's first wife, Diana Dill.
By the time Eric reached adulthood, Michael had already established a successful film career.
Eric won a place at the Royal Academy of Dramatic Arts in 1980. He ignored his father's advice to seek digs at the local YMCA and checked into the Dorchester.
Although he managed to find some acting work after the course, the role he knew best was a drink and drug addict.
He lived up to the tag of black sheep of the family with a string of binges which led to aggression and several arrests.
Three years ago he sued his psychiatrist, claiming he had prescribed him cocktails of dangerous drugs that left him lame, disfigured and addicted.