To most of us it seems obvious that alcohol would cause more problems with aggression than cannabis: how many fistfights have you seen caused by people smoking a joint together? But cannabis isn't totally blameless, either, in terms of sparking negative encounters - after all, it can cause anxiety and paranoia in some users, which can manifest as aggressive outbursts.
A study conducted in the Netherlands and published in the journal Psychopharmacology investigated how each of the drugs affect "subjective aggression in alcohol and cannabis users, respectively, following aggression exposure."
Researchers followed 61 participants, 20 of which were heavy drinkers (defined as 21-50 alcoholic drinks a week for men, and 15-35 for women), and 21 of which were cannabis users. Participants were all in the 18-28 demographic.
Users in each group were given a dose of alcohol and placebo, or cannabis and placebo, respectively. Then, researchers had them do a "single category implicit association test," in which they matched positive and negative words to photos depicting aggressive behaviour. In the second test, a computer game, players were told they could win money by pressing buttons, then pitted them against an "adversary" (actually a computer - unbeknownst to the participants) who could mess with them by stealing their winnings.
Drinkers indeed proved more aggressive
Researchers predicted "aggression exposure would increase subjective aggression in alcohol users during alcohol intoxication, whereas it was expected to decrease subjective aggression in cannabis users during cannabis intoxication." And sure enough, not only did the alcohol group behave more aggressively while drunk than sober, the cannabis group less aggressive when they were high.
The findings held true in the self-assessments as well: alcohol users rated themselves as more aggressive while drunk, and tried harder to undermine the computer game. The smokers were less aggressive in their attempts to win the money.
All of this is, as iCitizen puts it, "in line with other research. A study in 2014, for instance, found that marijuana use among couples was linked to lower rates of domestic violence. In a fun study from the 1980s, researchers gave undergraduates varying doses of marijuana and then asked them to administer electric shocks to people in another room. The more high the undergrads were, the less interested they were in zapping other people."
All this should encourage heavy boozers to engage in a bit of deep breathing the next time they find themselves getting riled up, as well as proving the old saying: booze kills, cannabis chills.