Children or teens who experience chronic anxiety may be more likely to consume cannabis heavily later on in life, according to a new study that sheds some light on the complex relationship between cannabis and mental health.

Researchers from the Duke University School of Medicine tracked residents of western North Carolina for more than 20 years. Participants were as young as nine years old when the surveying began, and they were monitored in areas like mental health, education, job attainment and use of drugs and alcohol.

The researchers found that among young adults with “problematic” cannabis consumption habits – in other words, daily use that meets diagnostic standards for addiction – more than a quarter had experienced serious anxiety in childhood or adolescence.

The data covered 1,229 participants and researchers focused on problematic cannabis use among those aged 19 to 21 and those aged 26 to 30.

While 76.3 percent didn’t develop problematic consumption habits during that period, almost a quarter experienced issues that the researchers categorized as: 1) limited problems, 2) persistent problems, and 3) delayed problems.

Those who were classified as having limited problems represented 13 percent of all problematic consumers. This group tended to experience issues with cannabis before the age of 16 or in their late teens or early 20s, but curbed their use as they got older. This group also had the most family conflict and childhood instability, but their circumstances improved after they left home.

"They didn't have as many children at a young age," lead author Sherika Hill said in a press release, "and they went further in their education when they were 19 to 21 compared to those with persistent and delayed profiles."

Those classified as being persistent users represented seven percent of all problematic consumers. They tended toward getting into trouble as young as nine years old, and their consumption continued through early adulthood. Roughly a quarter of this group had anxiety disorders in childhood and between the ages of 19 and 21.

Members of this group were also most likely to suffer from psychiatric disorders or enter the criminal justice system. Most of their friends were drug users, as well.

"This suggests that a focus on mental health and well-being could go a long way to prevent the most problematic use," Hill said.

Those classified as having delayed problems represented four percent of problematic users and only started experiencing problems with cannabis between the ages of 26 and 30. More than half of this group had been bullied or mistreated as children. That said, this group experienced less anxiety, alcohol use and use of hard drugs compared to those who smoked cannabis from a young age.

Black participants were five times as likely as white participants to end up in this category.

"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."

Hill said these findings present an opportunity to develop better-rounded ways of tackling this problem at different ages.

"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."

h/t Tonic: VICE