Twins Study Finds No Evidence That Marijuana Lowers IQ In Teens

UNITED KINGDOM: Roughly half of Americans use marijuana at some point in their lives, and many start as teenagers. Although some studies suggest the drug could harm the maturing adolescent brain, the true risk is controversial. Now, in the first study of its kind, scientists have analyzed long-term marijuana use in teens, comparing IQ changes in twin siblings who either used or abstained from marijuana for 10 years. After taking environmental factors into account, the scientists found no measurable link between marijuana use and lower IQ.

“This is a very well-conducted study … and a welcome addition to the literature,” says Valerie Curran, a psychopharmacologist at the University College London. She and her colleagues reached “broadly the same conclusions” in a separate, non-twin study of more than2000 British teenagers, published earlier this month in the Journal of Psychopharmacology, she says. But, warning that the study has important limitations, George Patton, a psychiatric epidemiologist at the University of Melbourne in Australia, adds that it in no way proves that marijuana—particularly heavy, or chronic use —is safe for teenagers.

Most studies that linked marijuana to cognitive deficits, such as memory loss and low IQ, looked at a single “snapshot” in time, says statistician Nicholas Jackson of the University of Southern California in Los Angeles, lead author of the new work. That makes it impossible to tell which came first: drug use or poor cognitive performance. “It’s a classic chicken-egg scenario,” he says.

 

Laws Make Studying Marijuana Difficult

DELAWARE: The only marijuana available for research in the U.S. is locked down by federal regulators who are more focused on studies to keep people off the drug than helping researchers learn how it might be beneficial.

Marijuana is a trend that “will peak like tobacco then people will see their error,” said Nora Volkow, director of the National Institute on Drug Abuse, which serves as the gatekeeper for U.S. marijuana research through its oversight of a pot farm that grows the only plants that can be used in clinical trials.

Meanwhile, marijuana advocates say NIDA’s control over research has made almost impossible their ability to test the drug against ailments such as pain, cancer-related nausea and epilepsy.

The federal researchers aren’t “set up to study potential medical benefits, so it’s inappropriate for NIDA to have a monopoly on supply,” said Dan Riffle, director of federal policies at the Marijuana Policy Project, a Washington-based group that lobbies to change marijuana laws.