DENVER - The first two states to legalize recreational marijuana are starting to grapple with teenagers' growing use of highly potent pot, even as both boost the industry and reap huge tax windfalls from its sales.

Though the legal purchase age is 21 in Colorado and Washington, parents, educators and physicians say youths are easily getting hold of edibles infused with tetrahydrocannabinol, or THC, the psychoactive component that causes a high, and concentrates such as "shatter," a brittle, honey-colored substance that is heated and then inhaled through a special device.

Each poses serious risks to adolescents' physical and mental health.

"Underage kids have unbelievable access to nuclear-strength weed," said Andrew Brandt, a Boulder, Colorado, software executive whose son got hooked while in high school.

With some marijuana products averaging 68% THC - exponentially greater than the pot baby boomers once smoked - calls to poison control centers and visits to emergency rooms have risen. In the Denver area, visits to Children's Hospital Colorado facilities for treatment of cyclic vomiting, paranoia, psychosis and other acute cannabis-related symptoms jumped to 777 in 2015, from 161 in 2005.

The increase was most notable in the years following legalization of medical sales in 2009 and retail use in 2014, according to a study in the Journal of Adolescent Health published in 2018.

"Horrible things are happening to kids," said psychiatrist Libby Stuyt, who treats teens in southwestern Colorado and has studied the health impacts of high-potency marijuana. "I see increased problems with psychosis, with addiction, with suicide, with depression and anxiety."

It is unclear whether all of this means years of generally stagnant pot use among children are coming to an end. Surveys finding little change with pot since 2014 "may not reliably reflect the impact of legalization on adolescent health," the authors of that 2018 study concluded.

Washington's latest Healthy Youth Survey showed 20% of eighth graders and nearly half of seniors "perceive little risk of regular marijuana use." Many teens consider it less risky than alcohol or cigarettes.

As more than a dozen states from Hawaii to New Hampshire consider legalizing marijuana, doctors warn of an urgent need for better education - not just of teens but of parents and lawmakers - about how the products being marketed can significantly affect young people's brain development.

The limited scientific research to date shows that earlier and more frequent use of high-THC cannabis puts adolescents at greater jeopardy of substance use disorders, mental health issues and poor school performance.

"The brain is abnormally vulnerable during adolescence," said Staci Gruber, an associate professor of psychiatry at Harvard Medical School who studies how marijuana affects the brain. "Policy seems to have outpaced science, and in the best of all possible worlds, science would allow us to set policy."

The critics also insist that more must be done to maintain tight regulation of the industry. That's not been the case so far, they argue, with dispensaries opening near high schools in Seattle and with retail and medical pot shops in Denver outnumbering Starbucks and McDonald's locations combined.

The bills that passed this spring in each state's legislature, with bipartisan support, aimed mostly for industry expansion or deregulation. Washington lawmakers lightened the consequences of administrative violations, allowing for written warnings in lieu of fines. Colorado lawmakers approved broader investment in marijuana businesses and home delivery for medicinal users - followed by delivery for recreational users in 2021. Colorado also gave the go-ahead for consumers to use the drug in licensed dispensaries, restaurants and theaters.

Some physicians liken the states' actions to a public health experiment, one that supports the cannabis industry's interests while ignoring the implications for adolescents' health.

"I hope we don't lose a generation of people before we become clear we need to protect our kids' brains," said Leslie Walker-Harding, an adolescent medicine specialist who chairs the pediatrics department at Seattle Children's Hospital. It also is seeing more teens with marijuana-related symptoms.

The industry disagrees that potent products like crumble, budder and crystalline are a danger, saying additional studies are needed. Existing data are "inconclusive about whether the changes that have been linked to early cannabis use are damaging in the long term," Morgan Fox, media relations director for the National Cannabis Industry Association, said in an email. "There also needs to be more research on whether potency actually has an impact on consumers."

What's not disputed is how much is on the line financially. Ten states and the District of Columbia - with Illinois poised to be next - allow recreational marijuana use for adults, and 34 permit medical marijuana. Washington's commercial market posted a record $978 million in retail sales in fiscal 2018, data show, which meant $358 million in excise tax for state coffers. Colorado's pot industry racked up even higher sales in calendar 2018: a record $1.54 billion, which brought in $266 million in marijuana taxes, licenses and fees.

Colorado state Rep. Jonathan Singer, a Democrat from the community of Longmont, north of Boulder, expects the new delivery law to help block teens from buying marijuana via online and other easy sources. "We are in many ways stamping out a black market that doesn't care whether they sell to kids," he said in an interview.

Yet many educators and parents worry the opposite will occur: that the most recent measures will make it even easier for adolescents to get cannabis.

"It seems like everyone is looking the other way, and meanwhile kids are ending up in hospitals," Brandt said in detailing the struggles over his son's marijuana use. After the 20-year-old college student's grades plummeted in the fall, his father enrolled him in a private treatment program costing thousands of dollars a month.

The popularity of cannabis concentrates - which bear no resemblance to the plant from which they're derived - is linked to teens' burgeoning use of electronic cigarettes, according to school officials. Some e-cigarette devices work with marijuana as well as nicotine. Unlike a burning joint, the vaped pot is odorless and smokeless.

The crossover is evident in Montrose, a recreation hub nestled in the Uncompahgre Valley on Colorado's western slope. A 2017 national survey ranked Colorado at the top of 37 states for high schoolers' use of e-cigarettes, with a state survey that same year finding that more adolescents here vape than in any other region.

Vaping is an escalating disciplinary issue for Principal Scot Brown, a burly, no-nonsense administrator who has led Olathe Middle and High School for 11 years. He keeps the evidence in his "confiscation drawer."

"This is from a four-day period," he said recently, yanking open the drawer to reveal about a dozen vape pens and other devices. One was an angular gold-and-black teardrop-shaped gadget he found in a kid's wallet. "Almost 50 percent of my students have vaped, whether it's nicotine or marijuana. It's an epidemic."

Brown is hardly the only Montrose educator alarmed about students vaping cannabis. Matt Jenkins, who coordinates special education programs for the school district, mobilized after seeing students "going into the stratosphere, getting beyond way too high." He obtained a $750,000 grant, funded by state marijuana tax revenue, to hire two social workers and a nurse to help with "the Pandora's box we opened."

Jenkins quips that the district is "using weed money to tell the kids not to use weed" - and to prevent or reduce substance abuse. Its strategies include events that bring together students, parents, public health officials and even former users, as happened on a misty morning last month at Olathe.

In the school's cavernous gym, back-to-back assemblies were introduced to a 40-year-old author, speaker and drug-treatment consultant named Ben Cort. Clad in a blazer and jeans, he paced the floor and talked about how he'd kicked his marijuana habit as a teen - and why that was so important.

Cort explained which part of the brain controls which function. He focused on the frontal lobe, the area instrumental in problem solving, memory, language and judgment. Not until a person's mid-20s is it fully developed, he stressed.

"Think about it this way: Your brain is my phone - it's still growing and getting strong enough to handle everything the world will throw at it," he said, lifting his black cellphone high over his head. "When you put THC in it," Cort paused and flung the phone to the floor, eliciting gasps.

What will happen? he asked. His audience shouted the answer: "It will break!"

"Right," he responded. "The bottom line is, weed ain't for kids in any form - eating it, vaping it, smoking it. It's not okay."

The students bombarded him with questions: Is weed addictive? Is what it does to a teen's brain actually visible on a scan? Can you overdose on it? His answer, again and again and again: yes.

Cort conceded afterward that his talks with young people are often the hardest. They think they know so much more than they do, he said, and don't realize how vulnerable they are in a world of ever-more-powerful pot. The same applies to any state where pot is legal, he maintains.

"We are holding on to a construct of marijuana which today is antiquated," he said. "Ten years from now, there's going to be a reckoning."

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