Alan O'Neill died from drinking too much and from the injuries he suffered in a nasty fall.
The L.A. County Coroner's Office confirms the "Sons of Anarchy" actor died of chronic alcohol overconsumption. According to the Coroner's report ... other significant factors in his death include blunt force head trauma and heart disease.
The Coroner's Office tells TMZ ... O'Neill had fallen at home while drunk. The death has been ruled an accident.
We broke the story ... O'Neill's girlfriend found his body when she went to his home on June 6.
The Irish-born actor had been working steadily in Hollywood since the '90s. Most notably, he played Hugh on seasons 6 and 7 of "Sons of Anarchy," ... as well as Keith McGrath in "Fair City."
His cause of death was first reported by People.
Alan was 47.