Researchers at the Yale University of Medicine and Pennsylvania State University showed that trial participants who smoked marijuana tended to be more hostile and impulsive the day they used marijuana, as well as the day after.
According to Yale and Pennsylvania State researchers, 43 trial participants were analyzed over a 14-day period to determine how they responded to marijuana, alcohol, and tobacco. After controlling for certain factors, and removing alcohol and tobacco from the equation, researchers observed that marijuana users demonstrated an increase in hostile and impulsive behavior the day they used the drug and the following day.
The ultimate conclusion of these researchers was that the behavioral impact of marijuana warrants additional research, especially in light of the expansion of recreational marijuana in some states.
It is worth noting that 43 patients can hardly be described as representative of the U.S. adult population, which totaled roughly 245 million people as of 2014. Just because marijuana users in this small sample proved more hostile, it doesn't guarantee that marijuana was the cause, which is why additional studies are needed.
Nonetheless, it does place yet another obstacle in marijuana's possible path to nationwide legalization. We don't want to be a grumpy nation!