Ryan's death last month at the age of 53 led to reports that he had abused drugs and they were a cause of his passing.
However, the toxicology report from the coroner's office reveals that Ryan had no illicit drugs in his system and that he had died of a massive heart attack.
Ryan was found dead in his Dublin apartment by his girlfriend after he failed to turn up for his radio show.
His death sparked a massive period of mourning for Ryan, who had a daily radio program on the main Irish radio station. His funeral was attended by thousands.
A full post mortem and a toxicology screening was carried out after the death. They revealed that Ryan had died of a heart attack sometime during the night and had been dead for several hours when the body was found.