Multnomah County epidemiologist Julia Dilley found a drop in teenage marijuana use in Washington.

FILE PHOTO - Two teenagers can be seen smoking tobacco in a park in this file photo .The passage of legal marijuana laws doesn't necessarily mean more teenagers are puffing, according to a new study by Multnomah County's epidemiologist.

In fact, the report by the county, the Oregon Health Authority and other groups found a small but statistically significant drop in pot use by eighth and tenth graders in Washington between 2014 and 2016 — just a few years after the state legalized marijuana in 2012. The recreational market in Oregon's neighbor to the north opened for business in July, 2014.

But Julia Dilley, the county's epidemiologist and a senior research scientist with the state of Oregon's public health division, isn't ready to declare the case closed.

"This is a really early snapshot of what happened," she said in an interview. "I think it's going to take a while to know what happens to kids who grow up in a legalized context."

COURTESY PHOTO - Dr. Julia DilleyThe study used data harvested by the Washington State Healthy Youth Survey, which randomly polls public school students every two years. Dilley says she was inspired to examine the issue after seeing much-hyped coverage of a rise in teen pot use in Washington based on a 2017 scientific study.

The 2017 study was based on a different collection of data, the national teenage behavior survey Monitoring the Future, which Dilley says oversamples rural populations and isn't truly representative of the state. She says Monitoring the Future polls about 2,500 youth — compared with the roughly 50,000 respondents in her data set.

Moving forward, the big unknowns for Dilley include what products — and at what price point — will be on the market in the long term. There could also be certain "hidden" populations, who react to marijuana legalization differently based on location, age or socioeconomic status.

"There might be different effects for different kinds of kids," she said. "There's still more work to do and we have to keep paying attention to it."

Spaced-out smokers dumped some $82.2 million into state coffers in the last fiscal year, thanks to Oregon's 17 percent recreational cannabis sales tax. That's a habit that lawmakers could find hard to kick — no matter what public health consequences are ultimately revealed.