Adults who smoke marijuana often cut back after becoming parents – but they don’t necessarily quit.

The influence of a significant other and positive attitudes toward the drug overall, in addition to the onset of parenthood, also are factors in whether someone uses marijuana.

“When it comes to adults, we don’t know long–term consequences of moderate marijuana use in the legal context, so that we cannot say that we absolutely must intervene,” explained Marina Epstein, a UW research scientist and lead author of the study. “However, when it comes to parents, their use is strongly related to their children’s marijuana use, and that is a significant problem, since adolescent marijuana use can be harmful. Our study wanted to prepare us to build effective interventions for all adults if it becomes an issue.”

The study, published online May 19 in the journal Prevention Science, surveyed 808 adults (parents and nonparents), a group the SDRG first identified as fifth–graders at Seattle elementary schools in the 1980s as part of a long–term research project. For the marijuana study, participants were interviewed at specific intervals over a 12–year period, ending when most participants were 39 years old. That survey concluded in 2014 — two years after marijuana was legalized in Washington. A parent–only subset of 383 people was surveyed at separate times, ending in 2011, just before the statewide vote that gave rise to pot shops.

Women and people of color made up approximately half the big study pool; of the parent subsample, about 60 percent were women, and an equivalent percentage were people of color.

The increasing availability of marijuana, along with shifting societal opinions about it, lends a timeliness to the findings and provides potential for further study, Epstein said. What factors affect behavior, especially among parents? Past studies have linked parenthood with decreased marijuana use; what makes this one different is the examination of other influences, too, and how those might inform intervention strategies.

More than half of Americans now support legalizing marijuana, according to a 2015 Pew Research Center report, and data from 2014 indicate a majority of Americans view alcohol as more damaging to a person’s health than pot.

Meanwhile, concerns about the health effects of marijuana tend to focus on children and teens – years when the brain is still developing. The Centers for Disease Control and Prevention and the National Institute on Drug Abuse stress the potential for long–term cognitive impairment, problems with attention and coordination and other risk–taking behaviors due to heavy marijuana use. For those reasons, medical professionals recommend that parents avoid using marijuana – or drinking heavily – around kids to prevent modeling the behavior.

The UW research found that, in general, a greater percentage of nonparents reported using marijuana in the past year than parents. At age 27, for example, 40 percent of nonparents said they had smoked pot, compared to about 25 percent of parents. By participants’ early 30s, their marijuana use had declined, but a gap between the two groups remained: Slightly more than 16 percent of parents said they smoked pot in the past year, while 31 percent of nonparents reported the same.

But the study also showed that participants who started using marijuana as young adults were much more likely to continue to use into their mid– to late 30s, even after they became parents. Having a partner who used marijuana also increased the likelihood of participants’ continued use. Those trends were true of both parents and nonparents, demonstrating the impact of attitudes and the behavior of others, Epstein said.