What Pot Does to a Teen’s Brain

By DR. SUSHRUT JANGI

These days, it’s decidedly uncool to criticize marijuana and the rush toward legalization. So far, 29 states and the District of Columbia allow medical marijuana, while nine states and DC permit recreational use. Sixty-one percent of Americans say they believe the drug should be legal, according to a recent Pew Research Center survey.

But underscoring this incredible momentum for legalization is the misconception that marijuana can’t hurt anybody. It can—especially young people. The myth that cannabis, another name for the plant, is not habitforming is constantly challenged by physicians. “There’s no question at all that marijuana is addictive,” Sharon Levy, MD, tells me. She is the director of the Adolescent Substance Abuse Program at Boston Children’s Hospital, one of a few programs designed to preemptively identify substance-use problems in teens. Anyone can get hooked, but about one of every six teens who smoke marijuana will become addicted, research shows.

One of Dr. Levy’s patients was an 18-year-old who started smoking pot several times a day in tenth grade. She dropped out of high school, was fired from several jobs, and stole money from her parents. “She and her family were at their wits’ end trying to find appropriate treatment in a health-care system that doesn’t consider addiction to marijuana a serious problem,” Dr. Levy says. “We are simply not prepared for the fallout of marijuana legalization.”

Yet we don’t hear this perspective very often. Why not? “People strongly defend marijuana because they don’t want legalization to be derailed,” says Jodi Gilman, PHD, an assistant professor at Harvard Medical School with the Center for Addiction Medicine. Big money is at stake. All told, the states that have legalized the drug raked in an estimated $1 billion in taxes for 2017. A recent study projected that if marijuana were legal in all 50 states, it would produce $46 billion in federal sales tax revenue and more than one million jobs by 2025.

Last year, teen marijuana use went up significantly for the first time in seven years, according to a large annual study conducted by the University of Michigan. The latest National Survey on Drug Use and Health, completed in 2016, also showed an increase, while tobacco and alcohol use continued to decrease.

“If you go into a high school and ask the classroom, ‘Are cigarettes harmful? Is alcohol harmful?’ every kid raises their hand,” Gilman says. “But

“If I ask kids, ‘Is marijuana harmful?’ not a hand goes up,” says Jodi Gilman, PHD, of Harvard.

SUSHRUT JANGI, MD, is an internist and instructor in medicine at Beth Israel Deaconess Medical Center in Boston.

if I ask, ‘Is marijuana harmful?’ not a hand goes up.” In fact, more than half of 10th and 12th graders say they believe pot isn’t dangerous, according to a report from the RAND Corporation, a nonpartisan research organization. “That is an unintended consequence of legalization,” Pam Luna, a RAND consultant, told NPR. Or maybe it is intended. Pot proponents often argue that one reason to legalize the drug is so its dosage and potency can be regulated.

You might compare public perception now to the way people used to feel about tobacco. In the 1950s, nearly half of Americans smoked tobacco. Meanwhile, the big tobacco companies aggressively used their lobbying power to deceive the public about the harms of smoking and to forestall regulation by the Food and Drug Administration. Of course, now we know that tobacco causes cancer, heart disease, and other health problems, and cigarette packaging carries mandatory warnings.

To bring balance to a narrative driven by pro-legalization campaigns, Gilman and others are interested in leveraging data to show pot’s real effects. In 2014, Gilman published research on 18-to-25-year-olds that showed differences in the brain’s reward system between users and nonusers. Teens who smoked marijuana had significant abnormalities in the areas of the brain linked to emotion, motivation, and decision making (see sidebar below). “I got a lot of hate mail after that,” she says.

In another study, Gilman found that teens who smoked marijuana

daily showed long-term memory loss in adulthood—even years after they’d stopped. Heavy use can result in a loss of six IQ points, about the same dip that lead poisoning causes, according to the American Psychological Association. In other studies, the brains of young adult pot smokers have shown deterioration in the language areas, with more verbal memory decline among those who started at the youngest ages.

The key ingredient in marijuana, tetrahydrocannabinol (THC), attaches to brain receptors that modulate healthy behaviors such as eating, learning, and forming relationships. Over time, THC rewires this whole cognitive system, throwing off its finely tuned balance. Early evidence in mice has shown that repeated exposure to THC causes these receptors to disappear altogether.

The results can be lasting and detrimental. Teens who frequently smoked pot, especially young men, were less likely to hold full-time jobs as adults, get married, or finish their education, a University of Connecticut study found. Young adults are three times more likely than others to drive under the influence of cannabis, which is the illicit drug most often detected in crashes (often combined with alcohol). Numerous studies have shown that its use impairs driving and increases the risk of a crash. Since the drug was legalized in Colorado, related visits to emergency rooms and urgent care centers have increased almost threefold among those under 21.

It’s worth bearing in mind that it was science that eventually curtailed the power of Big Tobacco and prevented nearly 800,000 cancer deaths in the United States between 1975 and 2000. As marijuana marches toward the same legal status as cigarettes, its potential hazards will require equal attention by science. (The National Institutes of Health is beginning a ten-year study of the effects of alcohol and drugs, as well as screen time, nutrition, and exercise, on the adolescent brain. So far, more than 7,600 adolescents have enrolled.)

The argument here isn’t whether marijuana should be legal. There are champions on either side of that debate. Instead, should the drug become widely available, it’s to our detriment to blindly consider legalization a victory. We must be cautious when societal shifts can affect health, especially among our most vulnerable.

Teens who frequently smoked pot were less likely to hold full-time jobs as adults.