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Perception of marijuana as 'safe drug' is scientifically inaccurate

Teresa Tanoos's picture
Teenage pot smokers at greater risk of damaging brain

Marijuana is the most popular illegal drug used worldwide, according to the first-ever global survey of illicit drug abuse, and it is the most used illicit drug by teenagers because they perceive pot as a safe drug.

However, the nature of the teenage brain makes users of marijuana among this population especially at risk for developing addictive behaviors and suffering other long-term negative consequences, say researchers involved in another study at the University of Montreal and New York's Icahn School of Medicine at Mount Sinai.

"Of the illicit drugs, cannabis is most used by teenagers since it is perceived by many to be of little harm. This perception has led to a growing number of states approving its legalization and increased accessibility. Most of the debates and ensuing policies regarding cannabis were done without consideration of its impact on one of the most vulnerable population, namely teens, or without consideration of scientific data," wrote Professor Didier Jutras-Aswad of the University of Montreal and Yasmin Hurd, MD, PhD, of Mount Sinai.

"While it is clear that more systematic scientific studies are needed to understand the long-term impact of adolescent cannabis exposure on brain and behavior, the current evidence suggests that it has a far-reaching influence on adult addictive behaviors particularly for certain subsets of vulnerable individuals."

For this study, researchers examined over 120 studies that reviewed different aspects of the relationship between cannabis and the adolescent brain. Their review included the biology of the brain, the chemical reaction that occurs in the brain when the drug is used, the influence of genetics and environmental factors, as well as various studies into the "gateway drug" phenomenon.

"Data from epidemiological studies have repeatedly shown an association between cannabis use and subsequent addiction to heavy drugs and psychosis (i.e. schizophrenia),” explained Dr. Jutras-Aswad.

“Interestingly, the risk to develop such disorders after cannabis exposure is not the same for all individuals and is correlated with genetic factors, the intensity of cannabis use and the age at which it occurs. When the first exposure occurs in younger versus older adolescents, the impact of cannabis seems to be worse in regard to many outcomes such as mental health, education attainment, delinquency and ability to conform to adult role," Jutras-Aswad added.

While it’s challenging to verify for certain a causal link between drug consumption and the resulting behavior, the researchers said that rat models enable them to explore and directly observe the same chemical reactions that happen in human brains.

Marijuana interacts with the brain via chemical receptors, which are situated in the part of the brain that controls learning, as well as management of rewards, motivated behavior, decision-making, habit formation and motor function.

Prior to adulthood, while the structure of the brain is rapidly changing during adolescence, researchers believe that using marijuana at this time significantly influences a teen user's portion of the brain that has to do with the development of their personality. In adolescent rat models, for example, researchers have observed differences in the chemical pathways that govern addiction and vulnerability. Specifically, a receptor in the brain called the dopamine D2 receptor is significantly lacking in cases of substance abuse.

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According to NIDA's 2012 Monitoring the Future study, about 6.5 percent of 8th graders, 17.0 percent of 10th graders, and 22.9 percent of 12th graders had used marijuana in the month before the survey. In fact, marijuana use declined from the late 1990s through about 2007.

Unfortunately, this trend appears to be reversing. Since 2007, annual, monthly, and daily marijuana use increased among 10th and 12th graders while daily use increased among 8th graders. In 2012, 6.5 percent of 12th graders reported using marijuana daily, compared to 5.1 percent in 2007.

However, only an approximate one in four teenage users of cannabis become addicted or dependent on the drug, which suggests to the researchers that specific genetic and behavioral factors have more of an impact on whether teenage pot use will continue.

Studies have also shown that cannabis dependence can be inherited through the genes that produce the cannabinoid receptors, as well as an enzyme involved in the processing of THC. There are about 400 other chemicals that are also in marijuana that can also affect health, but THC is the main psychoactive, or mind altering, ingredient.

There are also psychological factors that are likely involved in cannabis dependence.

"Individuals who will develop cannabis dependence generally report a temperament characterized by negative affect, aggressivity and impulsivity, from an early age. Some of these traits are often exacerbated with years of cannabis use, which suggests that users become trapped in a vicious cycle of self-medication, which in turn becomes a dependence," Dr. Jutras-Aswad said.

While a lot remains unknown about the mechanics of cannabis abuse, the researchers emphasize that a body of research exists that proves there are clear consequences involved for teenagers who use and abuse marijuana.

"It is now clear from the scientific data that cannabis is not harmless to the adolescent brain, specifically those who are most vulnerable from a genetic or psychological standpoint. Identifying these vulnerable adolescents, including through genetic or psychological screening, may be critical for prevention and early intervention of addiction and psychiatric disorders related to cannabis use. The objective is not to fuel the debate about whether cannabis is good or bad, but instead to identify those individuals who might most suffer from its deleterious effects and provide adequate measures to prevent this risk," Jutras-Aswad said.

"Continuing research should be performed to inform public policy in this area. Without such systematic, evidenced-based research to understand the long-term effects of cannabis on the developing brain, not only the legal status of cannabis will be determined on uncertain ground, but we will not be able to innovate effective treatments such as the medicinal use of cannabis plant components that might be beneficial for treating specific disorders," Dr. Hurd added.

Marijuana also may affect your mental health. Studies show that early marijuana use may increase your risk of developing psychosis if you have a genetic vulnerability to the disease. Psychosis is a severe mental disorder in which there is a loss of contact with reality, including false ideas (or delusions) about what is happening – and/or seeing or hearing things that aren’t there (hallucinations).

Marijuana also has been associated with depression and anxiety, but more research is necessary to confirm and better understand that relationship.

1. Neuropharmacology, "Trajectory of adolescent cannabis use on addiction vulnerability" (published online August 14, 2012), Doi: 10.1016/j.neuropharm.2013.07.028
2. The National Institute on Drug Abuse (NIDA), a component of the National Institutes of Health (NIH), “Drug Facts” (updated July 13, 2013).