Heroin and other opiate consumption was significantly and positively related to violent crime in 8 out of 19 models (42%), but negatively related in 4 out of 19 models (21%). In addition, opiate consumption was positively related to nonviolent offending in 16 out of 40 models (40%). At the study level, a much greater proportion of studies reported a PoC that was as predicted for nonviolent offending (55%) than for violent offending (27%). These findings suggest, as we expected, that opiate use is not a differential predictor of violence. They are consistent with the proposition that heroin users will often engage in expropriative crime to secure money for drugs. However, the association between opiate use and violent crime occurred at a greater than chance frequency, so that association cannot be dismissed. In just one study where violent and nonviolent offenders were compared, violent offenders reported more opiate use (Webster et al., 2010).
Turning to the “other illegal drug” category in which we combine the models that test illegal drugs other than marijuana, cocaine, crack, or heroin, we see that the use of these drugs was positively and significantly related to violent crime in 10 out of 17 models (59%), and negatively related in only 2 out of 17 models (12%). Other drug consumption was similarly associated with nonviolent offending (60% of coefficients). At the study level, the percentage of supportive studies was slightly higher for nonviolent than violent. (Two out of six studies of violence were supportive while three out of six studies using nonviolent offending reported a PoC that was significant.) There were just 2 studies that compared violent to nonviolent offenders. One of them reported a PoC where violent offenders had a higher usage of these “other” drugs than nonviolent offenders (Webster et al., 2010) and the other did not (Martin & Bryant, 2001). There is yet no indication that this vague category, including drugs such as amphetamines, sedatives, barbiturates, PCP, etc., distinguishes between violent and nonviolent offenders.