More than a half million U.S. adults participated in the survey over a dozen years, and the responses show a shift in attitude. Only a third of adults in 2014 said they thought weekly marijuana use was dangerous, down from half of adults in 2002.
That runs counter to scientific research about pot, said Dr. Wilson Compton, lead author of the study published online Wednesday by the journal Lancet Psychiatry.
“If anything, science has shown an increasing risk that we weren’t as aware of years ago,” said Compton, deputy director of the National Institute on Drug Abuse.
Other research has increasingly linked marijuana use to mental impairment, and early, heavy use by people with certain genes to increased risk of developing psychosis, he noted.
Some highlights of the report, which compared 2002 to 2014:
— About 1 in 8 adults said they used marijuana in the past year, up from 1 in 10. The number of marijuana users grew to about 32 million.
— Daily use doubled, to 3.5 percent or about 8.4 million U.S. adults
— Changes in marijuana use and perception began to really climb in 2006-2007.
— No increase was seen in reported marijuana use disorders, like impaired memory, difficulty thinking and withdrawal symptoms like cravings, sleeplessness and depression.
That’s surprising since law enforcement officials say marijuana is more potent than in the past, wrote Australian researcher Wayne Hall in an editorial in the journal.
More use should mean more reports of marijuana-related disorders. Another U.S. survey did find such an increase in recent years, Hall noted.
“I agree that this is a puzzle,” and needs to be researched further, Compton said.
Marijuana use remains illegal under federal law. Twenty-five states and the District of Columbia have medical marijuana laws, and starting in 2014, Colorado and Washington began allowing recreational sales. Alaska and Oregon now also allow sales without a doctor’s note.
Hall said it’s likely those changes will increase the use of marijuana and perhaps reports of disorders.
The study didn’t report on kids, only those 18 and older. But research drawn from another large survey has shown marijuana use among high school students has been falling. Over two decades, it dropped from 25 percent to about 22 percent.
Why are fewer kids using pot at a time more and more adults are?
There could be a lag. Youths have said in surveys that it seemed to be getting harder in the last decade to get marijuana. But that may change as more states legalize the drug, more adults use it, and if teens get into less trouble if caught with the drug, experts said.