Substance use at any age has consequences. Studies frequently cite the negative impacts—and occasionally tout some benefits of limited consumption—of alcohol and marijuana.

What is less known is how patterns of alcohol or marijuana use in one phase of life can affect the next generation, even long after an individual has stopped using.

A new study by the University of Washington's Social Development Research Group shows how a parent's use of marijuana, past or present, can influence their child's substance use and well-being.

"The really important takeaway is that parent history of marijuana use is an important risk factor for kids," said Marina Epstein, lead author of the study and a project director at the SDRG, which is part of the UW School of Social Work.

The study, published online September 9 in the journal Psychology of Addictive Behaviors, builds off previous work that had grouped participants according to whether, when and how often they used, and examined impacts to their health and behavior. That study found four distinct patterns: "nonusers"; "adolescent-limited" (confined to only that period of life); "late onset" (starting in their late teens, early 20s); and "chronic" (ongoing and frequent). This study is based on a subset of the original participants who have become parents, and has linked parents' past use of marijuana to their children's use of and attitudes toward alcohol and marijuana, other problem behavior, and school achievement.

The original investigation involving parents began in the 1980s when the now-adults were in fifth grade at several Seattle elementary schools. Researchers have followed the participants ever since. In 2002, when the participants were 27, SDRG recruited those who had become parents and began interviewing their children about alcohol beginning at age 6, and marijuana starting at age 10. To date, 360 children completed interviews between the ages of 10 and 20.

Children and teens of chronic users were most likely to use alcohol and marijuana themselves, as researchers had predicted. But what came as more of a surprise was the behavior of children whose parents had primarily used during adolescence: Compared to the children of nonusers, children of adults in the "adolescent-limited" group were more than 2.5 times as likely to use marijuana and 1.8 times as likely to use alcohol. This was true even after parents' current marijuana use was accounted for.

In comparison, children of chronic users were nearly 4.5 times as likely to use marijuana, and 2.75 times as likely to use alcohol, as children of nonusers.

Children in the "late-onset" group, as it turned out, were least likely to use marijuana, as were children of nonusers. They did, however, have lower grades.

"Using marijuana in adolescence is associated with a host of other problems in the present and later into adulthood," said Epstein, who was the lead author on the earlier paper that established the marijuana usage patterns. "Now we see that echoing through to their children."

According to that prior study, people who used marijuana during their teen years tended to have poorer functioning during the period in which they were actively using, and, by their early 30s, to have lower academic and economic outcomes than people who started using as adults, or who never used.

Chronic users had the worst outcomes in terms of health and quality of life, Epstein added: Poor mental health, lower academic outcomes, less financial stability and greater tendency of criminal and/or risky behaviors were associated with frequent, lifetime marijuana use.

The researchers need additional studies to uncover reasons for the relatively high usage patterns among children in the adolescent-limited group. There may be a connection between a parent's use during adolescence, for example, and their subsequent attitudes toward substance use among teenagers in general, Epstein said.

Today, 33 states have legalized marijuana in some form, often for medical purposes, and of those, 11 states—including Washington—have legalized it for recreational use. Those developments have implications for how parents talk to their children about marijuana and how health care providers talk to patients. Even a routine review of a child's health history could include a question about a parent's history of marijuana use—just to consider the potential impact on the child, Epstein said.

"Now that marijuana is legal, we have to be able to talk to parents about how they're using, and to be more specific—how much, how often, whether this is lifelong pattern," said Epstein. "The landscape of marijuana is changing, and we have to be mindful of it."