It's pretty clear to most observers that marijuana use doesn't cause aggression. And yet some studies have found correlations between marijuana use and intimate partner violence (IPV). The problem, argues a team of researchers from SUNY Buffalo and Rutgers in a new paper in Psychology of Addictive Behaviors, is that these studies haven't been thorough enough to establish anything approaching tight causal links — for example, given the data from one of them, it's just as likely victims of IPV used marijuana to cope with the abuse they endured than that their marijuana use somehow led to it.
So the team ran a new study — one that they see as better designed to specifically suss out the effects of smoking pot — in which they examined 634 couples' first nine years of marriage, gathering data on their alcohol and pot consumption habits, antisocial behavior, and tendencies toward IPV. They found that "more frequent marijuana use by husbands and wives predicted less frequent IPV perpetration by husbands," and that husbands' marijuana use alone predicted less IPV perpetrated by wives. Moreover, "the strongest protective effect [was found] among couples in which both spouses used marijuana frequently."
Basically all their data, in other words, pointed in the direction of more pot, less domestic violence, with the one exception being a statistically significant correlation between marijuana use and IPV among only those wives who had already perpetrated IPV in the year before marriage (more research would need to be done to explain why this is).
Why would there be this inverse correlation? Ask any college freshman plucked off the street. Or, if you want to get fancier about it, let's hear from the researchers:
There are several possible reasons why we may have observed a protective association between marijuana use and IPV perpetration
in the current investigation. Among experienced users, marijuana may enhance positive affect (Hart et al., 2010), which in turn could reduce the likelihood of conflict and aggression. In addition, previous research has found that chronic users exhibit blunted emotional reaction to threat stimuli, which may also decrease the likelihood of aggressive behavior (Gruber, Rogowska, & Yurgelun-Todd, 2009).
It's unclear whether the use of "blunted" was unintentional or an example of extremely dry social-science-researcher cheekiness.