Marijuana and the Adolescent Brain

These days it’s hard to find anybody critical of marijuana. The drug enjoys broad acceptance by most Americans — 63 percent favored ending cannabis prohibition in a recent Quinnipiac poll — and legislators on both sides of the aisle are becoming more likely to endorse than condemn it. However, there are increasingly alarming studies about what pot does to the human brain especially the adolescent brain.

One of the many things my teen clients have told me they like about getting high, was using pot alleviated their boredom — to one of curiosity, stimulation and enhancement of every day activities, thereby creating an atmosphere of a carefree and “relaxed” attitude. They report that marijuana transforms the mundane into something dramatic: family outings, school, work or just sitting on the couch become endlessly entertaining. My often response to their professed state of boredom is to define boredom as the inability to be with one’s self.

Like any mind-altering substance, marijuana produces its effects by changing the rate of what is already going on in the brain. In this case, the active ingredient delta-9-THC substitutes for your own natural endocannabinoids and mimics their effects. It activates the same chemical processes the brain employs to modulate thoughts, emotions and experiences. These specific neurotransmitters, used in a targeted and judicious way, help us sort the relentless stream of inputs and flag the ones that should stand out from the torrent of neural activity coding stray thoughts, urges and experience. By flooding the entire brain, as opposed to select synapses, marijuana can make everything, including the most boring activities, take on a sparkling transcendence.

Why object to this enhancement? As one client told me, using pot made his personal and professional life more engrossing and thus made him, he thought, a better person and employee. Unfortunately, there are two important caveats from a neurobiological perspective. Widespread cannabinoid activity, by highlighting everything, conveys nothing. When using marijuana the brain dampens its intrinsic machinery to compensate for excessive stimulation. Chronic exposure ultimately impairs our ability to imbue value or importance to experiences that truly warrant it. In adults, such neuro-adjustment may hamper or derail a successful and otherwise fulfilling life, though these capacities will probably recover with abstinence. But the consequences of this desensitization are more profound, perhaps even permanent, for adolescent brains. 

Adolescence is a critical period of development, when brain cells are primed to undergo significant organizational changes: Some neural connections are proliferating and strengthening, while others are pared away – called pruning. Although studies have not found that legalizing or decriminalizing marijuana leads to increased use among adolescents, perhaps this is because it is already so popular. More teenagers now smoke marijuana than smoke products with nicotine; between 35 and 45 percent of high school seniors report smoking pot in the past year, about 25 percent got high in the past month, and about 6 – 8 percent admit to using virtually every day.

​The potential consequences are unlikely to be rare or trivial.The decade or so between puberty and brain maturation is a critical period of enhanced sensitivity to internal and external stimuli. Noticing and appreciating new ideas and experiences helps teens develop a sense of personal identity that will influence vocational, romantic and other decisions — and guide their life’s trajectory. Though a boring life is undoubtedly more tolerable when high, with repeated use of marijuana, natural stimuli, like those associated with goals or relationships, are unlikely to be as compelling. 

Smoking marijuana changes what is happening in a user’s brain. For teenagers, the effects may be permanent. It’s not surprising, then, that heavy-smoking teens show evidence of reduced activity in brain circuits critical for flagging newsworthy experiences, are 60 percent less likely to graduate from high school, and are at substantially increased risk for addiction and alcoholism. Their motivation to accomplish any goals in life are can be significantly reduced. Recent data compiled from research conducted by neuroscientists is even more alarming: those who use THC, may be at increased risk for mental illness and addiction. The studies show alterations in cortical structures associated with impulsivity and negative moods.

Might the relationship between marijuana exposure and changes in brain and behavior be coincidence, as tobacco companies asserted about the link between cancer and smoking, or does THC cause these effects? Unfortunately, we can’t assign people to smoking and nonsmoking groups in experiments, but efforts are underway to follow a large sample of children across the course of adolescent development to study the effects of drug exposure, along with a host of other factors, on brain structure and function, so future studies will probably be able to answer this question. 

As a psychotherapist who specializes in treating clients with substance abuse and/or addiction, I’m unimpressed with many of the widely used arguments for the legalization of marijuana. “It’s natural!” So is arsenic. “It’s beneficial!” The best-documented medicinal effects of marijuana are achieved without the chemical compound that gets users high. “It’s not addictive!” This is false, because the brain adapts to marijuana as it does to all abused drugs, and these neural adjustments lead to tolerance, dependence and craving — the hallmarks of addiction.I have a difficult time listening to the astounding lack of skepticism about pot that is taking place in our current debate. Whether or not to legalize weed is the wrong question. The right one is: How will the increasingly use of marijuana affect individuals and communities? We are astoundingly naive about how the widespread use of pot will affect communities and individuals, particularly teenagers. 

Most drug legislation in this country had nothing do with scientific evidence of harm. Legalizing marijuana is inevitable, but don’t ignore the science on its dangers. Many people view marijuana as either benign or beneficial. Even many of those apathetic toward its potential health benefits are ecstatic about its commercial appeal, whether for personal profit or state tax revenue. In our rush to throw open the gate, we might want to pause to consider how well the political movement to legalize marijuana matches up with the science, which is producing inconveniently alarming studies about what pot does to the adolescent brain.

Though the evidence is far from complete, wishful thinking and widespread enthusiasm are no substitutes for careful consideration matches up with the science which is producing inconveniently alarming studies about what pot does to the adolescent brain. 


Thom Kessler, LMFT, RAS
[email protected]
415-454-8931