One of my coworker's friends recently asked her whether cannabis can make its consumer "grumpy," because sometimes he wakes up cranky after an evening of smoking. His timing was serendipitous, as I chanced upon a study from December 2014 that examined the effects of marijuana use on "impulsivity and hostility in daily life."
For this study, researchers from the Yale University School of Medicine's Department of Psychiatry and Penn State University's Department of Psychology collaborated to better understand whether cannabis use affected consumers' daily experiences. They found 43 participants with no substance dependence and asked them to report on their alcohol consumption, tobacco use, recreational cannabis use, impulsivity, and interpersonal hostility for a period of 14 days.
The participants were a mix of men and women who have previously consumed cannabis and had an alcoholic beverage at least once per week. They weren't substance dependent, nor did they use any substances aside from cannabis, alcohol, or nicotine. After a phone screening and intake interview, they completed a carbon monoxide test and provided urine samples before being trained on how to complete their daily assessments on a smartphone.
Each night, the participants were prompted to measure the following information:
Daily alcohol, tobacco, and cannabis use (how many drinks were consumed, how many cigarettes or cigars were used, and how many "hits" of cannabis were taken and the method of intake)
Daily impulsivity as logged by a 7-item short form survey using the "Barratt Impulsiveness Scale-Brief"
Daily interpersonal hostility in the form of a survey every time a subject had an interpersonal interaction lasting longer than five minutes
The data showed that impulsivity increased on days cannabis was used compared to days it wasn't used, and interpersonal hostility increased on use days as well.
"Our findings support a directional effect on marijuana use on increases in next day impulsivity, a result not previously described in the literature. This is consistent with prior research findings that occasional users of marijuana experience stronger effects of marijuana on attention and inhibition relative to chronic users (Theunissen et al., 2012)."
What's the science behind this conclusion? The researchers dive into that, too:
"Laboratory studies have found that individuals under the influence of marijuana displayed systematic changes in interpersonal behavior and experience, including a pattern of interpersonal withdrawal, hostility, and diminished interpersonal skills. Despite subjective reports of enhanced sensation and perception, individuals under acute administration of THC showed objective decreases in the number of interpersonal interactions engaged in and the expression of empathetic communications. This suggests that marijuana use has a significant impact on interpersonal behaviors, of which users are not aware. Additional research has found social-emotional deficits in marijuana users, and increases in hostility or aggression."
The study reports that chronic cannabis consumers have anterior cingulate cortex (ACC) and amygdala deactivation in response to "subconscious presentation of emotional faces," compared to a control group displaying increased activation. The ACC plays a role in error monitoring, behavioral correction, and inhibition when responding to contextual or environmental changes, so a deactivation of the ACC and the amygdala could "manifest as inappropriate interpersonal responses or altered perceptions of interpersonal behavior in others." In other words, chronic consumption can be deactivating the part of your brain that keeps your stinkface reaction in check.
So what's the downside to being a grumpypus? Well, according to researchers, impulsivity is associated with a higher risk for mental health issues, addiction disorders, and risky behavior, while hostility can be tied to cardiovascular risk, stress-related health dysfunction, troubled intimacy, and other aggressive behaviors.
The study, however, is not without flaws. The sample size is incredibly small, and researchers were unable to observe any effects of alcohol use on impulsivity or hostility, despite citing previous studies that have identified such effects (to be fair, another study was cited that also failed to find alcohol effects on risk-taking behavior, though five minutes on YouTube should lend credence to the idea that alcohol and risk-taking behavior are often related).
Second, the researchers conceded that "asking participants to rate their own behaviors may have promoted a level of self-awareness that subsequently impacts either interpersonal behaviors or ratings of behaviors," and that "future research should examine whether self-monitoring of interpersonal behaviors results in differences in actual behaviors." In other words, the participants could have been overly self-critical since they knew they had to log their daily behavior for this study. First, the researchers' primary predictor of interest was whether their subjects reported any cannabis use vs. specific doses, which, as we know, can vary considerably.
Finally, and quite possibly most amusingly, "…individuals may have been intoxicated while completing the surveys and this may have biased the responses for same day effects. Future research should examine whether level of intoxication changes these effects." Translation: Our subjects could have been super drunk or super stoned or both, so their self-reported data could be skewed.
So does cannabis make you grumpy or not? According to this study, yes, but as with all cannabis findings, more research is needed because the limited number of studies that exist are only able to tell us a partial story. Also, this study was narrow in its scope and flawed in its methodology, which is another reason why we need more research so we can test, re-test, and test some more until we're able to come to more confident conclusions. Re-scheduling cannabis would be a huge step in the right direction, as it would open up more research avenues.
Time for you to weigh in! In your personal experience, have you noticed your mood turning sour after chronic cannabis consumption, or is the outcome of this study the only thing making you angry right now?