Children are more likely to start using cannabis at a younger age if their mothers consumed the drug during their childhood, according to new research.

According to a study from the Harvard T.H. Chan School of Public Health, children were more likely to start using marijuana two years earlier than their peers if their mothers used the drug during the first 12 years of their life.

Natasha Sokol, one of the study’s lead investigators from Brown University’s School of Public Health, said they were interested in studying how adult consumption of cannabis may affect a child’s introduction to it in light of the current debate over legalization in North America.

“With legalization of adult use, there seems to be an increase, at least in the frequency, of parent marijuana use so we were really curious about exposure to marijuana use,” she told on Saturday.

The researchers analyzed two linked groups from The National Longitudinal Survey of Youth 1979, from the period of 1980 to 1998, and the Child and Young Adults survey, covering the period between 1988 to 2014, which comprised of data for 4,400 children and 2,586 mothers.

The study found that 2,983 children (67 per cent) and 1,053 mothers (35 per cent) in the groups self-identified as cannabis users. Those children with mothers who used marijuana during their childhoods began taking the drugs themselves at the median age of 16, the study said. On the other hand, the median age was two years later for the children of mothers who didn’t consume cannabis.

Because they were conducting a secondary data analysis, Sokol said they didn’t know if the children in the sample groups were aware of their parents’ marijuana use.

The study took into account other factors related to the child’s early life, behaviour and cognition, along with their family’s socioeconomic position and environment. The researchers also noted that the association was stronger among non-Hispanic, non-black children.

Given the current shift in attitudes towards the recreational and medicinal benefits of using marijuana, the authors said it’s important to identify potential factors that can contribute to children adopting cannabis us at a younger age, such as parental use of the drug.

“What we know is that early initiation of cannabis – so when kids and adolescents use cannabis – is associated with an increased likelihood of health consequences,” Sokol said.

“Incorporating maternal cannabis use into our understanding of the important risk factors for early initiation may help us better identify at-risk youth for more tailored or intensive prevention strategies.”

The study acknowledged that marijuana is generally thought to be less harmful than other drugs, such as opioids, and has been recognized for its therapeutic benefits for treating a number of different medical conditions in adults.

In children who are still developing, however, the drug has been associated with negative side effects, such as impairment in attention, concentration, decision-making, memory and an increased impulsivity, Sokol said. There has also been evidence to suggest that marijuana can cause a reduction in IQ that may persist in adulthood, according to the study.

The researchers suggested the children of marijuana-using parents may be an important identifiable group that could be at risk for early adoption of the drug. Although they didn’t have specific recommendations, the authors said the study’s findings could help marijuana prescribers and physicians educate parents who use cannabis about preventing early use for their children, such as decreasing their own use and reducing its visibility until their children are older.

“Given the neurocognitive, health, and social consequences associated with early use, delaying initiation may be an important, but undervalued, public health goal,” Sokol said.

The study has been published in the American Journal of Preventive Medicine.