As more states legalize both medicinal and recreational marijuana, researchers keep looking to understand who uses pot—and why. That means studying teens to figure out how and when people start smoking weed, but it also means looking at adults, some of whom develop a problematic habit. A new study that tracked participants for more than 20 years found that, of those whose marijuana use is considered problematic in early adulthood, more than a quarter had anxiety disorders in childhood or adolescence.
The findings come from Great Smoky Mountains Study, a long-term study of residents near the Appalachian Mountains in western North Carolina. Researchers there enrolled a cohort of children as young as 9 years old; many of those participants are now in their 30s. From 1993 to 2015, they were tracked on a number of areas of interest, including mental health, education, job attainment, and use of drugs and alcohol. (It's worth noting that in the 11 counties studied, Hispanics and Latinos are underrepresented and Native Americans are overrepresented, relative to the rest of the United States.)
Using data from 1,229 participants, researchers focused on what they classified as problematic marijuana use: daily consumption or a habit that meets diagnostic guidelines for addiction. They honed in on patterns of use from the college years (ages 19 to 21) into adulthood (ages 26 to 30).
More than three-quarters (76.3 percent) of those studied didn't develop a marijuana problem over that period. But almost a quarter did have issues, and researchers broke them down into three categories: those with limited problems, persistent problems, and delayed problems.
The three categories help us better understand how people use marijuana from adolescence into adulthood. The first category, limited users, represented 13 percent of all problematic users. They fit a familiar pattern: trouble with weed while in school before age 16 or in their late teens and early 20s, but their habits taper off as they got older. That group, researchers were somewhat surprised to find, had the highest level of family conflict and instability during childhood—factors often associated with more drug use.
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When they left home and got out on their own, they did better. "They didn't have as many children at a young age," Sherika Hill, the study's lead author and an adjunct faculty associate at the Duke University School of Medicine, said in a release, "and they went further in their education when they were 19 to 21 compared to those with persistent and delayed profiles."
The persistent users, 7 percent of the total, got into trouble early, as young as 9 years old. Their use continued into their late 20s and early 30s. Around a quarter of this group had anxiety disorders in both childhood (27 percent) and at ages 19 to 21 (23 percent). They had the highest rates of psychiatric disorders and were most likely to be involved in the criminal justice system. The majority of their friends were drug users, too, they said. That points to underlying issues that could contribute to their use. "This suggests that a focus on mental health and well-being could go a long way to prevent the most problematic use," Hill said.
Finally, a small group (4 percent) of adults went through adolescence and early adulthood (the peak time for most pot users) with no marijuana problems, only to then become habitual users between ages 26 and 30. This is the delayed group. More than half of them had been bullied by peers and mistreated by caregivers as children. Yet they also showed lower rates of anxiety, alcohol use, and use of other hard drugs compared to the persistent users who smoked weed from an early age. Black people were five times as likely as white people to wind up in this group. It's not clear why members of this group would turn to weed later in life. "One theory is that they were somewhat protected by having fewer peers in late adolescence who were substance users," Hill said, "but this is one of the questions we will continue to seek answers for."
The study is a good reminder that, for all the study of marijuana, there's still a lot we don't know about how it fits into and affects people's lives. Hill sees this as an opportunity to advance our understanding—and to devise smarter ways of handling the issue. "A lot of current interventions and policies in the US are aimed at early adolescent users," she said. "We have to start thinking about how we are going to address problematic use that may arise in a growing population of older users."
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