As states across the country legalize marijuana, the increase in the drug's usage has grown significantly. From 2001 to 2013, "marijuana use rose from 4.1 percent to 9.5 percent of the U.S. adult population," while 30 percent of that sizable smoking group meet the "criteria for addiction," according to the National Institutes of Health.
Given this sharp and significant rise, researchers sought to determine how pot users, when under the influence, relate to those around them. Or more specifically, they wanted to understand their ability to recognize the emotions of others. A recent study, led by Lucy Troup, a Colorado State University associate professor of psychology, found that cannabis users were less able to identify emotions and moods of those they came into contact with.
"We tried to see if our simple emotion-processing paradigm could be applied to people who use cannabis, because we wanted to see if there was a difference," said Troup, discussing her study with Colorado State.
With Colorado's 2012 passage of Amendment 64, cannabis became legal and dispensary shops opened statewide. This law, along with the diverse nature of past studies on the drug, caused Troup to take a closer look at marijuana's effects.
"We're not taking a pro or anti stance; but we just want to know, what does it do?" Troup said. "It's really about making sense of it."
She and her graduate students conducted nearly two years' of experiments on about 70 legal chronic-, moderate- and non-users of marijuana.
While connected to a brain scan, the study's volunteers were shown photographs of four different faces -- displaying angry, scared, happy and blank expressions. The cannabis users and non-users scored similarly in this "explicit" recognition exercise.
But when asked instead to pay attention to the sex of person's face and point out the emotion, cannabis users had far poorer scores than non-users. As the study found, this difference in "implicit" recognition -- one's ability to identify another's mood with little effort -- led researchers to believe that pot users have less ability for natural empathy than non-users.
The study essentially mirrors the findings of past studies. Dating as far back as 1979, researchers have theorized that cannabis adversely affects the interpersonal skills of its users.
These findings may also help explain observed links between cannabis use and psychosis. But those with already existing psychotic or schizophrenic traits may tend to use cannabis. Still, causation is not clearly known. Many studies -- observing hundreds to thousands of people over decades -- have found that cannabis use not only exacerbates these symptoms, but increases the chances of their development if used at an early age.
Troup's study, however, leaves open the possibility that users simply have a more limited attention span, which is problematic for reading emotions of others. As the study states, "Attention driven demands on emotion processing appear to be affected by cannabis use."
Troup is now turning her attention on another study using brain scans to see how cannabis use affects people with depression, anxiety and other mood disorders.