Marijuana Addiction is Growing and Teens Face the Highest Risk, Health Officials Say

As more states move to legalize its medicinal and recreational use, marijuana is becoming more addictive, public health officials warn, likely because of its rising potency, which has been engineered to placate habitual users and hook new ones.

Nearly 9 percent of marijuana users will become dependent on it, according to the National Institute on Drug Abuse, increasing to about 17 percent in those who started using it in their teens.

David Smith, a physician who treats drug abuse, told The Washington Post that selective breeding of the cannabis plant can up its content of tetrahydrocannabinol (THC)—the psychoactive ingredient that gets users high—which could increase its addictive properties, particularly among young people.

"Back in the day when kids were sitting around smoking a joint, the THC levels found in marijuana averaged from 2 to 4 percent," Smith told the Post. "That's what most parents think is going on today. And that's why society thinks marijuana is harmless."

Selective breeding emerged to meet the demands of marijuana connoisseurs who seek strains with higher levels of THC once they've maxed out their tolerance. For traditionally grown marijuana, higher THC content means less variegated cannabinoids, which produce the distinct flavors and aromas of different strains. With genetic modification, growers can pick out desired traits in the plant's genotype, in the same way crop producers engineer corn to resist pests.

In 1995, the average potency of cannabis peaked at 4 percent, then 12 percent in 2014. THC levels have climbed sharply since. As of 2018, average potency hit 20 percent, but that's not the limit: increasingly popular marijuana extracts, known as "dabs," contain anywhere from 40 to 80 percent THC, a Drug Enforcement Administration report stated.

A man lights a joint at a pro-marijuana demonstration on May 12 in Paris. Marijuana addiction is on the rise as its potency climbs, public health officials warn. (Photo by Thomas Samson/AFP/Getty Images)

Potency spikes have been suggested to cause physical harm. A 2016 study pointed to higher THC levels as a possible explanation for the 53 percent increase in marijuana-related emergency transports of teenage males between 2005 and 2010. Chronic teen use was also tied to poor school performance and lower overall life achievement, greater likelihood of car accidents and chronic lung inflammation.

Though little is known about the compound's effects on the brain, studies have found it lights up the brain's reward center by raising dopamine levels and altering nerve firing, two characteristics of addictive drugs. Chronic marijuana use lowers sensitivity to THC, which furthers the demand for strains with higher potency, according to a report from the California Society of Addictive Medicine. Addiction symptoms mirror those of other drugs, too, such as physical and psychological dependence, though no overdoses have proved fatal.

Researchers have long maintained that teens were more likely to become addicted to marijuana and suffer cognitive delays as a result. In 2013, psychologists posited that weekly use could interfere with adolescent brain development and damage memory and problem-solving abilities.

Even retail pot can contain harmful materials. In Colorado, one of the pioneering states to legalize recreational marijuana, investigators found products crawling with contaminants like fungi, which crowded some marijuana flowers with 1 million spores. Marijuana concentrates were even more concerning: Inspectors found solvents like butane, which can affect the central nervous system. Most of the products sold in stores contained only trace amounts of cannabidiol (CBD), the compound that lends marijuana its medicinal value.

"These samples are representational, I think, of what's happening here in the state and, probably, across the country," Andy LaFrate, who heads a lab that tests marijuana potency, told NBC News in 2016. "Because most of the new states coming online with medical or retail marijuana have people from Colorado coming in to set up those markets."