Past research has indicated that couples who abuse substances are at a greater risk for divorce, in part because substance abuse often leads to an increase in domestic violence.

However, new research has found that when it comes to marijuana use, the opposite might be true: frequent use of marijuana by couples is associated with less partner violence.

Researchers from Yale University, University of Buffalo and Rutgers recruited 634 couples from 1996 to 1999 while they were applying for a marriage license in New York State. After an initial interview, the researchers followed the couples over the course of nine years using mail-in surveys to measure the effects of marijuana use on intimate partner violence (IPV).

The study defines IPV as acts of physical aggression, such as slapping, hitting, beating and choking, and it was measured by asking couples to report violence committed by them or toward them in the last year.

At the end of the first year, 37.1 percent of husbands had committed acts of domestic violence.

Marijuana use was measured by asking participants how often they used marijuana or hashish (defined as pot, weed, reefer, hash, hash oil or grass) in the last year. Participants were also asked about other drug use including alcohol, because, as the researchers explain the study, marijuana and alcohol are often used in conjunction.

What the researchers found surprised them: due to the fact that alcohol and other substances are known to increase domestic violence, they hypothesized that marijuana use would have the same effect. But that was not the case.

"More frequent marijuana use generally predicted less frequent IPV for both men and women over the first 9 years of marriage," the researchers wrote. Not only that, couples who both used marijuana frequently -- compared to one spouse using it more than the other -- were at the lowest risk for subsequent partner violence.

Why would marijuana be different than other substances? Researchers hypothesize that the positive side effects of using marijuana may actually reduce conflict and aggression. They note that previous research has found chronic marijuana use to blunt emotional reactions, which could in turn decrease violent or aggressive behavior between spouses.

Are you surprised by these findings? Let us know in the comments!

Clarification: Language has been amended to better characterize the relative frequency of incidences of partner violence relative to marijuana use.