It may be viewed as a mellow drug, but a new study from the Yale School of Medicine calls that widely accepted perception about pot into question. Marijuana use can lead to increased impulsivity and perception of hostility in oneself and others, according to the study, published online in the journal Drug and Alcohol Dependence on Jan. 14.The study’s findings come as Connecticut and states across the nation debate whether they should join the slowly-growing ranks of states that have legalized the drug.
Forty-three participants monitored their recreational use of marijuana, alcohol and tobacco over a 14-day period using their smartphones. Impulsivity and hostility were measured by responses to an Ecological Momentary Assessment on the participants’ phones.
“There are effects of recreational use on the psyche that last, for example, the finding that impulsivity lasted into the next day,” said Rajita Sinha GRD ’92, the study’s senior author and professor of psychiatry. “It is not just an acute effect. There are more lasting effects of marijuana use.”
The study’s lead author, professor of psychiatry Emily Ansell, said she was surprised that the effect on impulsivity after smoking marijuana lasted into the next day, while alcohol use did not lead to impulsivity. She explained their statistical analysis allowed each participant to act as his or her own control, so the changes in impulsivity were measured relative to days when the participant did not use marijuana. The change in impulsivity that the researchers observed was acute and temporary, lasting into the day after use, Ansell added.
Sinha said that perceiving hostility in oneself and others makes sense — as a mild hallucinogen, marijuana changes perception. She also noted that the use of EMA was key in allowing participants to record their behaviors without having to go to a lab. Coming into a lab can often affect participants’ behaviors, skewing study results.
The EMA has been widely used and validated in the field of substance abuse, Ansell said. The researchers conducted a statistical analysis to ensure that the act of responding to the EMA did not interfere with participants’ actions. While researchers initially worried that having participants check in on the EMA could increase their awareness of their behaviors and make them less likely to smoke marijuana, drink alcohol and smoke cigarettes, the analysis showed that the app use did not decrease users’ consumption rates.
Yasmin Hurd, professor of psychiatry, neuroscience and pharmacology at Mount Sinai Hospital — who was not involved in the research — said the study was novel in its ability to capture behaviors outside of the laboratory. She added that more human studies like these are needed to better understand the findings of animal studies.
“Animal studies can give us causality regarding a specific drug or behavior, but we can never ask an animal how they feel,” she said. “We can judge specific phenotypes related to psychiatric vulnerability, but I think being able to carry out these studies in humans is really important to gain insights into what features of their marijuana abuse we should be studying in animal models.”
Sinha said this study also serves as a reminder that neither alcohol nor marijuana is better than the other — they are both drugs, but simply act in different ways.
Ansell said she plans to conduct a similar study with a larger sample and also investigate if these results hold amongst a group of habitual and non-recreational marijuana users. Sinha plans to continue to investigate psychosocial and decision making changes resulting from marijuana through stress test measures. While many people believe that marijuana can help combat anxiety disorders, she thinks it may make the problem worse in the long term.
Hurd, meanwhile, praised the timeliness of the study.
“Research is really way behind the prevalent use of marijuana and increased legalization, so these human studies are extremely important because there are very few of them,” Hurd said. “The work is novel in this aspect. Using smartphone technology is also a very innovative aspect of this real-world understanding of drug use from this study.”
Four states have legalized marijuana for recreational use.