During the same time frame, the popularity of other forms of marijuana consumption rose. For example, the use of "edibles" rose fivefold -- from only about 2 percent of pot-using teens in 2015 to almost 10 percent two years later.
The popularity of "dabbing" -- smoking marijuana extracts or concentrates, not the raw leaf -- rose from 4.3 percent of teen pot users in 2015 to 7.6 percent by 2017, according to the team led by Kayla Tormohlen of the Johns Hopkins Bloomberg School of Public Health, in Baltimore.
The rate of vaped pot remained relatively steady, however: 5.1 percent in 2015 and 4 percent in 2017.
There's potential good news and bad news from the new findings, Tormohlen's group believes.
The good news: The reduction in the popularity of smoked marijuana "could indicate that adolescents are choosing not to smoke or [are] using nonsmoking modes because of the associated health risks of smoking," the study authors wrote in the Aug. 5 online issue of JAMA Pediatrics.
But the bad news is that other modes of ingestion -- edibles and dabbing, especially -- can be risky due to higher levels of potency.
Different modes of pot ingestion carry "unique psychoactive associations, and potential harms," the study authors explained, "including unintentional overconsumption of edibles and an increased physiological tolerance and withdrawal associated with the high tetrahydrocannabinol [THC] levels of cannabis concentrates used for dabbing."
THC is the chemical in marijuana that provides users with a high.
Tormohlen's group noted that similar trends may be happening elsewhere, but "Colorado is one of the few states that collects statewide data on modes of marijuana consumption among adolescents."