Marijuana, the most common illegal drug in the United States, is increasing in popularity among the nation’s youth. The trend bodes ill for the future, suggests new research that is the first to show even “casual” smoking of marijuana—as infrequently as once a week—is linked to major changes in the brain.
In the study, a team of researchers from Northwestern University in Illinois, Harvard Medical School in Boston, and Massachusetts General Hospital used MRI to measure the volume, shape, and density of the amygdala and nucleus accumbens, two brain structures related to emotion, reward, and motivation. The scans revealed abnormalities in these structures among young adults ages 18 to 25 who smoked pot at least weekly.
“People think a little recreational use shouldn’t cause a problem, if someone is doing OK with work or school,” said Hans Breiter, one of the co-authors and a psychiatry professor at Northwestern. “Our data directly says this is not the case.”
Appearing in an April issue of The Journal of Neuroscience, the study adds to a body of research suggesting pot leaves a long-term mark on the brain, especially among younger users. A New Zealand study published in 2012 found that people who began smoking marijuana heavily as teenagers lost an average of eight IQ points between the ages of 13 and 38. Other research has found marijuana users have fewer brain connections in regions responsible for memory and learning.
Some skeptical researchers say the association between weed and IQ could be the fault of other potential factors, like personality or socioeconomic status. But if the hypothesis is true that pot dulls mental abilities, we should pay attention to another trend: Teenagers are becoming more likely to believe the drug is safe.
A Department of Health and Human Services survey released in December 2013 found that a declining number of American high-school seniors—only 40 percent—believe regular marijuana use is harmful (in 2012, 44 percent thought so). A quarter of seniors have smoked weed in the past month, and 7 percent smoke it daily—up from 2 percent in 1993. More than one in 10 eighth-graders have used marijuana in the past year.
The more open-minded teen attitudes toward marijuana have no doubt been encouraged by the push toward legalization. Twenty-one states, plus the District of Columbia, now permit marijuana for medicinal purposes. Washington and Colorado already allow recreational use.
In states with medical marijuana laws, one-third of 12th-graders who use pot say they sometimes obtain it from somebody with a medical marijuana prescription. According to the National Institute on Drug Abuse, around 9 percent of those users will eventually become addicted. Add in the decline in IQ, and we have the ingredients of a social experiment with generational consequences.
Within five years, the world’s first deep ocean mining operation could kick into gear nearly a mile beneath Pacific waters. Mining company Nautilus Minerals resolved a lengthy dispute with Papua New Guinea, and plans to begin grinding gold, silver, and copper from the ocean floor off the nation’s northern coast, using robotic underwater machines. Environmentalists worry about the unknown effect on ocean life. —D.J.D.