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.