Drugs and Alcohol: Findings and Research Needs
Similar to other reviewers, we conclude that the association between alcohol consumption and violence is very consistent, more consistent than the association between alcohol consumption and nonviolent offending, but we note that measures of alcohol intoxication are best for differentially predicting violence. In addition, our findings did not bear out the expectation that the prevalence of alcohol abuse would be higher among violent offenders than nonviolent offenders.
Before we outline the findings on drugs, we caution the reader about offender studies. Offender samples may not be the best way to test this research question due to the fact that drugs are illegal and enforcement agencies may be more inclined to make arrests for some types of drugs over others. We made this point earlier in this chapter.
On the whole, studies of “drug use” are more consistently associated with nonviolent offending than with violent offending. This was true for all subcategories of drug use (cocaine is less conclusive than the others). However, violent offenders are generally more likely to report drug use than nonviolent offenders, and the “drug use” measure emerges as the best differential predictor among the drug use measures.
Disaggregated analyses on the findings on marijuana as well as “other” drugs so far support the same pattern; marijuana use is slightly more consistently associated with nonviolent crime than it is with violent crime, but offender studies suggest that violent offenders are more likely to report marijuana use or test positive for marijuana use than nonviolent offenders. In one study where the authors controlled for other types of drug use, marijuana use emerged as consistently associated with violence. We believe this surprising finding should be directly evaluated in future research.
Although it has been argued that cocaine use may have a psychopharmacological influence on violent offending, it is also true that cocaine users are more likely to be arrested for nonviolent offending, making it difficult to disentangle any causal influence on violence. Our findings do not point to cocaine as a differential predictor of violence; in fact, one study where the authors controlled for alcohol and other drug use suggested that cocaine had a negative effect on violence (Martin & Bryant, 2001). Further research, focusing specifically on cocaine intoxication, using a sample that is unbiased by enforcement choices, is needed to see if the arguments made in psychopharmacological discussions of cocaine are borne out.
It has been argued that heroin and opiate use is much more likely to lead to property crime, used to gain income to buy these addictive drugs, than it is to lead to violence. Incidental violent crime is expected in the form of robbery and occasional assaults due to the rough drug trade. The studies of violent and nonviolent offending that we compared more consistently reported associations between heroin/opiate use and nonviolent offending than violent offending. However, a greater than chance number reported associations between heroin or opiate use and violent offending. Offender studies are yet inconclusive; nevertheless, we do not expect that heroin/opiate use will be a differential predictor of violence, and do not recommend future research on this point.
Since we would expect dose-response effects, or greater problems with violence among those who frequently use drugs, or are currently intoxicated, future research should attempt to measure drug use and intoxication with greater specificity. Casual use may not have effects on violence while abuse or addiction might have strong effects. More research on this point might help us understand when drug treatment or drug treatment court interventions would be worthwhile. Differentiating between drug types is important.
Distinguishing between types of violent crime might be important for drug research as well. In particular, more studies comparing the association between drug use and nonviolent crime to the association between drug use and robbery, and other types of violent crime such as assault, might teach us a great deal about the potential for this risk factor and our expectations for the crime reducing outcomes if we treat drug abuse.
Controlling for alcohol use and other drug use when testing the effect of any particular drug may be fruitful. Studies such as that reported by Martin and Bryant (2001), which attempt to disentangle the effects of several drugs, should be replicated; due to the model overspecification problem, we recommend comparing incremental models. Another important covariate may be mental health problems, as drug problems are sometimes comorbid with mental illness.