Study Finds Marijuana Can Be Harmful to Youngsters

A growing body of evidence suggests that the use of marijuana, or cannabis, can negatively impact the developing brains of approximately one in four adolescents, according to researchers at Icahn School of Medicine at Mount Sinai, and the University of Montreal.

The study, published in the August 16, 2013, issue of Neuropharmacology, highlights that the younger the user of cannabis, the more susceptible he or she is to delinquency, lower educational attainment, difficulty in conforming to an adult role, and mental health issues.

“Overall, it is impossible to ignore the evidence that cannabis is not harmless to the developing brain, but there remain large gaps of knowledge that need to be filled in order to help inform public policy,” says the study’s lead author, Yasmin Hurd, PhD, Professor of Psychiatry, Neuroscience, and Pharmacology and Systems Therapeutics at Icahn School of Medicine at Mount Sinai.

Dr. Hurd—also Director of Mount Sinai’s MD/PhD program—and her team analyzed 120 peer-reviewed studies on the impact of cannabis among teenagers. They examined chemical reactions in the brain, the influence of genetics and environmental factors, and the “gateway drug phenomenon,” where people begin to use other illegal drugs.

In addition, the investigators examined experimental animal models to directly explore the long-term behavioral and neurobiological consequences of the psychoactive ingredient in cannabis, THC, or tetrahydrocannabinol. They concluded that certain subsets of adolescents are at greater risk for developing negative mood and anxiety disorders, or making their existing disorders worse through regular cannabis use.

The high degree of neuroplasticity in the adolescent brain—characterized by a period of dynamic development—makes it particularly vulnerable to chemicals that may alter it. And teenagers, in general, are the likeliest population to experiment with marijuana. A recent study by the nonprofit organization The Partnership at found that nearly half of all teens have tried the drug, a 21 percent increase since 2008.

According to Dr. Hurd’s study, the majority of teenagers stop using cannabis as they mature into adulthood without migrating to other illegal drugs, suggesting there are differences in individual vulnerability.

With some states beginning to legalize marijuana for recreational and medicinal use, there is an unfortunate general perception that it is not as harmful as cigarette smoking or alcohol use, the researchers contend. Moreover, the debates and policies surrounding legalization are being done without consideration of scientific data or how it could impact teenagers, they add.

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