The Teen Brain on Cannabis

By: Spoony Quine — September 23, 2014

For decades in the twentieth century, many believed it was necessary to lie to teenagers about marijuana causing anything from violent behavior to Alzheimer’s disease-level effects on their brains in order to have anything really hair-raising to say against the stuff. However, in more recent years there has been a growing body of research showing that marijuana clearly prevents teens’ brains from developing properly, and that can be a real problem.


Although cannabis doesn’t seem to cause much damage to an adult brain, that may be so because the adult’s brain is no longer using its endocannabinoid system to grow profusely and in a precise manner. It is thought that adding extra cannabinoids distorts the neurological sculpting that goes on within the brain’s architecture.

There are a number of studies and reviews (i.e. Schneider 2008Wilson 2010Magnus 2008) that show the younger an adolescent starts using cannabis, and the more frequently, the more it negatively affects brain development. That includes noticeable changes to its physical structure, functionality of working memory and cognition, as well as more likelihood of the individual using drugs in the future.

The Wilson MRI study showed, for example, that subjects who had started using marijuana before age 17, versus those who started afterwards, had a smaller brain volume, as well as a smaller percentage of gray matter and a larger percentage of white matter. These subjects were overall smaller in both height and weight, showing that the effects are not confined to the brain.

One long-term study (Meier et al 2012) found that the bulk of cognitive impairment “was concentrated among adolescent-onset cannabis users, with more persistent use associated with greater decline. Further, cessation of cannabis use did not fully restore neuropsychological functioning among adolescent-onset cannabis users.” Thus, the authors concluded, cannabis must be neurotoxic to adolescents, therefore steps should be taken to prevent them from developing an early proclivity for ganja.

Other studies show that the earlier teens use cannabis, the more likely that certain individuals will develop psychosis later in life (Arseneault 2002), and that cannabis use appears to increase brain deformities linked to schizophrenia, including problems with working memory centers (Smith at al 2014). The link between pot and psychosis applies specifically to those who are genetically predisposed to schizophrenia (Caspi 2004), and is a reminder that some people are especially vulnerable to its effects.

The most recent analysis published in The Lancet (Silins et al 2014) focuses on the social and psychological effects of teen cannabis use, and has found that even occasional use appears to be problematic. This analysis integrates different studies from New Zealand and Australia, which found that the amount of cannabis use before age 17 correlates with later life outcomes at up to age 30.

Correcting for a variety of confounding factors, toking before 17 correlated with less likelihood of completing high school, getting a university degree, and more likelihood of depression, suicide attempts, and other drug problems such as cannabis dependence. Marijuana use was measured ranging from less than monthly to every day, and the more students used it, the more likely they were to have these outcomes.

There are probably multiple reasons for this, besides physical brain wiring problems: For example, students may be stigmatized by their superiors for doing drugs, and also, being convicted for possessing illegal drugs is enough to disqualify them for college financial aid. In other words, there are social reasons why they may find college entry particularly difficult, and perhaps much else.

And why do teens get into drugs in the first place? One significant factor appears to be child maltreatment, particularly occurring in adolescence, which impairs the ability for self-control and healthy emotional attachment to others. Teens may help themselves feel ‘normal’ by self-medicating with drugs such as marijuana, which is a known treatment for mood disorders. Whatever the root motivation of their marijuana use, these students could probably use more emotional support and psychological help rather than be demonized or arrested for their ‘bad behavior’.

Adding to such demonization include mass media reactions from pop psychologists like Drew Pinski, who said that the results of Silins et al is evidence that marijuana is just as addictive as opiates. He even labels everyone who smokes pot every day as a ‘marijuana addict’ — not surprising since his business is addiction.

Though physical dependence is possible for only about 9% of cannabis users, such ‘addicts’ face withdrawal symptoms including depressed mood, anxiety, reduced appetite, sweatiness, fever, and headache. They do not, as with opiates, involve vomiting, severely trembling, or screaming and crying for another hit. To conflate marijuana with opiates is a serious mistake, and surely Dr. Drew knows this.

Although opponents of more liberal cannabis laws may draw attention to such studies, it should be noted that increased cannabis use does not equal fewer high school graduates in general. For example, the National Survey of Drug Use and Health shows absolutely no correlation between teen marijuana use and graduation rates on a state level. Apparently, there are many other factors at play when it comes to completing high school.

Another point to consider is that teenagers are no more likely to use cannabis when it is made medically legal in any state (Choo 2013Anderson 2014), meaning that more legality does not seem to encourage more use. Similarly, what about drugs that are already legal and readily available? It’s important to note that the negative effects of alcohol on the developing teen brain are more pronounced than, and different from, the effects of marijuana use (i.e. Squeglia 2013Thoma 2010).

A recent study of high school seniors (Palamar et al) comparing the effects of alcohol and marijuana use shows that adverse outcomes were reported more commonly with alcohol use than marijuana, and even moreso with the use of both. Each drug was more likely to produce specific adverse effects. To quote the paper:

“Compared to alcohol use, marijuana use was more commonly reported to compromise relationships with teachers or supervisors, result in less energy or interest, and result in lower school or job performance.” This is not surprising, considering that marijuana is frequently associated with young people questioning authority. Frequent use also correlated more with more trouble with the police, which would make sense if one associates oneself with the illegal black market.

Also, “Compared to marijuana use, alcohol was more commonly reported to compromise relationships with friends and significant others; it was also reported to lead to more regret” for irrational behavior, and to cause problems in thinking clearly, and more likely to lead to driving while intoxicated. So, if teen marijuana use is such a concern, then surely teen alcohol use is even moreso? Yet, not many opponents of cannabis legalization are rushing to bring back Prohibition.

In any case, teenagers should be advised to let their brains grow unimpeded by alcohol or marijuana, or any other potentially detrimental drug. They should also seek other help besides self-medication if the need arises: Maltreatment at home, school, or from culture as a whole is challenging enough damage to a sensitive, growing brain.

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