More people support marijuana use, but they are frequently misinformed about the drug’s dangers and its addictive nature, said Nora D. Volkow, MD, director of the National Institute on Drug Abuse. She spoke at a March 8 congressional briefing in Washington, D.C.

Her talk, part of the “Friends of NIDA” series co-sponsored by APA, gave congressional aides and policymakers the latest research findings on marijuana’s harms and benefits. One-third of Americans have tried marijuana at least once, Volkow said, making it the most commonly used illegal drug in the United States — and a prime target for research. NIDA estimates that about 9 percent of frequent marijuana users are dependent on the drug.

“People take marijuana for the same reason they take other drugs: They make you feel good,” Volkow said.

That good feeling is tied to the dopamine-based reward system in the brain’s nucleus accumbens region. Compounds in marijuana bind to the brain’s cannabinoid receptors, triggering dopamine release and resulting in a high. Long-term use of marijuana not only increases the amount of the drug that users need to reach the same high, it also inhibits the brain’s natural cannabinoids. As a result, over time users feel dysphoric and “off” if they haven’t recently taken marijuana. Marijuana also targets and interferes with cannabinoid receptors in areas of the brain crucial to a number of cognitive functions, especially the cerebellum (movement), hippocampus (memory) and amygdala (emotional control).

Interfering with those cognitive processes is particularly dangerous for young people’s developing brains, Volkow said, and there’s evidence to suggest using marijuana at an early age can have lifetime consequences. Twin studies show that people exposed to marijuana as young teens are more likely to become dependent on other drugs, such as cocaine and painkillers.

Volkow said the pro-marijuana lobby’s work to legalize marijuana and the growing national support for using the drug for medicinal purposes are dangerous because many teenagers now view it as a “safe” drug, despite the fact that marijuana’s health effects aren’t well-known. A recent NIDA report shows that for the first time since the late 1970s, more 12th-graders are smoking marijuana than cigarettes — and marijuana is much stronger today than it was back then, Volkow said. Fellow panelist Alan Budney, PhD, a clinical psychologist who studies addiction at the University of Arkansas for Medical Sciences, said that it’s time to start rigorously developing an anti-marijuana campaign. Meanwhile, few studies have explored whether behavioral therapies work for marijuana addiction. Budney’s lab is developing a “contingency management” therapy that gives marijuana users incentives to quit. They’ve had success in some populations, he said, but the treatment needs to be culturally translated for more diverse populations.

—M. Price