Background and objective Alcohol abuse is common in the USA and is a well-established risk factor for violence. Other drug use and criminal activity are risk factors as well and frequently occur together with alcohol abuse. Firearm ownership is also common; there are >50 million firearm owners in the USA. This study assesses the relationships between alcohol and drug abuse and future violence among firearm owners, which no prior research has done.

Design and study population This records-based retrospective cohort study will involve all persons who legally purchased handguns in California in 2001—approximately 116 000 individuals—with follow-up through the end of 2013.

Methods The principal exposures include prior convictions for alcohol-related and drug-related offenses. The primary outcome measure is an arrest following handgun purchase for a violent Crime Index offense: homicide, rape, robbery or aggravated assault. Subjects will be considered at risk for outcome events for only as long as their residence in California can be established independently of outcome events. Covariates include individual characteristics (eg, age, sex, criminal history, firearm purchase history) and community characteristics (eg, demographics, socioeconomic measures, firearm ownership and alcohol outlet density). We will employ survival analytic methods, expressing effects as HRs.

Discussion The results of this large-scale study are likely to be generalisable and to have important implications for violence prevention policies and programmes.