Drugs, guns, and violent crime in California.

Background: There is evidence linking use of controlled substances with perpetration of interpersonal violence. While the United States constitution protects the right to own a firearm, federal law prohibits firearm purchase and possession by persons believed to be at high risk for violence, including those who use controlled substances unlawfully.

Methods: We report here the results of a 13-year prospective observational study on the risk of violent crime associated with a history of criminal drug charges in a cohort of 79,678 legal purchasers of handguns in California in 2001. The main outcomes were post-purchase charges for any violent crime, violent Crime Index crimes (murder, rape, robbery, aggravated assault), and firearm-related violent crimes. The main exposure of interest was a history of pre-purchase charge(s) for drug-related offenses; we examined as a secondary exposure a history of marijuana-related charges. We estimated adjusted hazard ratios (aHR) with 95 % confidence intervals (CI) using Cox proportional hazards multiple events models.

Results: We found that legal handgun purchasers in California with a history of drug-related charges, even those with marijuana charges only, had triple the risk of a post-purchase violent crime charge compared to purchasers with no criminal charges (drug charges only: aHR=2.9, 95 % CI 2.2-3.8; marijuana charges only: aHR=3.3, 95 % CI 1.8-6.0). In addition, a criminal history of drug charges only vs. no criminal history was associated with increased risk of one or more violent crime charges after the first post-purchase arrest event (aHR=1.6, 95 % CI 1.2-2.3).

Conclusion: It is incumbent on researchers and policy makers to understand the nature and causes of this risk in order to take effective steps towards mitigation.