(Reuters Health) - When mom uses marijuana, kids are more likely to try the drug at a younger age, a new study shows.

When mothers used cannabis during the first 12 years of a child’s life, there was a 40 percent higher likelihood the kid would start using the drug earlier than peers whose moms weren’t using, researchers reported in the American Journal of Preventive Medicine.

On average, children whose mothers used marijuana tried it themselves an average of two years earlier than peers whose mothers didn’t use the drug.

That puts those kids at risk for a host of marijuana-linked problems, said lead study author Natasha Sokol, who was a doctoral student at the Harvard T.H. Chan School of Public Health when the research was done.

Kids with mothers who used marijuana were at increased risk of starting to use the drug themselves before age 17. Their peers were more likely to start at 18.

The time between 16 and 18 “is a critical period of development,” said Sokol, who is now at the Center for Alcohol and Addiction Studies at the Brown University School of Public Health. “Marijuana might be disrupting certain aspects of brain development, including the development of the endocannabinoid system. It’s been associated with depression and, in predisposed individuals, there seems to be an increased risk of the development of psychosis.”

Marijuana use at this age can also affect a child’s ability learn, Sokol said. “Missing school or functioning at a lower level in school is a big deal,” she said. “Especially if it’s for an extended period of time.”

Sokol and colleagues analyzed data from participants in the National Longitudinal Survey of Youth and their biological children who signed on for the NLSY Child and Young Adults survey. The NLSY is a nationally representative survey that included 12,686 individuals living in the U.S. in 1979 between the ages of 14 and 21. NLSY participants were interviewed annually up until 1994 and then biennially after that. Out of 4,440 mother-child pairs identified by the researchers, 2,983 children, or 67 percent, and 1,053 moms, or 35 percent, said they used marijuana.

One limitation of the study, Sokol said, is the researchers didn’t have information on whether the kids knew their moms were using cannabis.

While that is a limitation of the study, “we also know that children are much more aware than we think they are,” said Dr. Michael Lynch, a toxicologist and emergency medicine physician and medical director of the Pittsburgh Poison Center at the University of Pittsburgh Medical Center. “That’s been proven again and again.”

Lynch said he wasn’t surprised to see children imitating behaviors modeled by their parents. But, “it’s nice to have a peer-reviewed work that identifies the risk that children are more likely to start using marijuana if they grow up in homes with a mother who uses the drug,” he added.

The findings are “concerning” Lynch said. “That’s because it’s in the context of expanding use and a more permissive culture around marijuana use,” he added. “All - even proponents - agree that younger initiation is unhealthy. That’s been fairly well studied, from an academic and career standpoint and from a cognitive development standpoint.”

Moreover, Lynch said, people who start marijuana at a younger age are at greater risk of addiction to either marijuana or prescription opioids.

“The finding is important but not surprising,” said Dr. Salomeh Keyhani, a professor of medicine at the University of California, San Francisco. “Studies of maternal tobacco smoking and adolescent initiation have had similar findings.”

“The results are particularly concerning given the unresolved debate on the association of adolescent use of cannabis and decreases in IQ,” Keyhani said. “The results are also concerning because there is no coordinated public health campaign that is informing the public of the potential risks of cannabis use.”

Sokol hopes her new findings won’t be misused.

“I don’t think this study needs to be evidence against legalization,” she said. “That’s not a successful public health policy.”

SOURCE: bit.ly/2Q3DvJ2 American Journal of Preventive Medicine, online September 24, 2018.