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Evidence of Youth Marijuana Use — What Every Mom Should Know

This is a special guest post by Trey Dyer of Equipping patients and families with the best information, resources, and tools to overcome addiction and lead a lifelong recovery.
Marijuana is the most commonly used drug among youth and adults in the United States. According to the 2015 edition of Monitoring the Future — a study by researchers at the University of Michigan that measures substance use among 8th-, 10th-, and 12th-graders — 15.5 percent of 8th-graders, 31.10 percent of 10th-graders, and 44.70 percent of 12th-graders reported using marijuana at least once in their lifetime. Roughly 1.1 percent of 8th-graders,3 percent of 10th-graders, and 6 percent of 12th-graders reported daily marijuana use, according to the study.

Today’s marijuana is more potent and widely available than ever before. A study by researchers at the University of Mississippi measured THC (the chemical substance in marijuana that produces “highs”) content among over 46,000 samples from 1993 to 2008 and found that the average percentage of THC content in marijuana was 8.8 percent in 2008, up from 3.4 percent in 1993.

Greater marijuana potency can cause a number of severe problems for users or exacerbate conditions that already exist. Teens who use marijuana greatly increase their risks of drug addiction, psychiatric disorder and long-term mental impairment.


“Marijuana is not addictive,” is a much-cited myth by supporters of recreational legalization of marijuana.However this is simply not true. About 9 percent of marijuana users become dependent on the substance, according to a study by researchers at the National Institute on Drug Abuse. The rate of addiction increases to 25 to 50 percent for daily marijuana users.

The risk of marijuana use disorder is higher when use begins during adolescence. One in six teenagers who use marijuana will become addicted to it. According to the National Survey on Drug Use and Health, 2.7 million adolescents 12 or older met the criteria for marijuana use disorder in 2012.

Psychiatric Disorders

Results from studies around the world suggest there is a strong link between marijuana use and mental illness. Symptoms of psychosis, both temporary and long-term, frequently occur in marijuana users. Many individuals with mental disorders turn to marijuana to cope with symptoms of their illness. However the severity of many mental illnesses is only exacerbated by cannabis use.

Researchers at the University of Oulu in Finland interviewed more than 6,000 teens aged 15 to 16and found that teens who use marijuana are more likely to “suffer psychotic symptoms and have a greater risk of developing schizophrenia in later life.”

Individuals with mental illness are seven times more likely to use marijuana and ten times more likely to have a marijuana use disorder, according to a review of U.S. data by researchers at Toronto’s Centre for Addiction and Mental Health. Rates of marijuana use were substantially higher among those with bipolar disorder, personality disorder and other substance use disorders.


Depression is one of the most common disorders among individuals with co-occurring mental and marijuana use disorders. Marijuana use can worsen depression, according to a report by the Office of National Drug Control Policy. Teens who smoke marijuana have double the risk of developing depression. Conversely, depressed teens are two times as likely to use marijuana or develop a marijuana use disorder. Teens who use marijuana at least once a month are three times as likely to have suicidal thoughts as their peers who do not.


Results from multiple studies suggest that marijuana may increase the odds of developing schizophrenia, exacerbate schizophrenic symptoms and cause schizophrenic-relapse among those with schizophrenia. A study by researchers at Yale University found that THC can also induce schizophrenic symptoms in otherwise healthy individuals.

Four out of five individuals with schizophrenia were frequent marijuana users when they were teenagers, according to a study by researchers at New South Wales Mental Health Review Tribunal in Australia. Approximately 75 to 80 percent of study participants habitually used marijuana between the ages of 12 and 21.

A study by researchers at the University of New South Wales suggests that marijuana use can also accelerate the onset of schizophrenia by nearly three years, causing earlier development of the disease than in those who do not use cannabis. According to the researchers, young individuals who regularly use marijuana increase their chances of developing schizophrenia in their lifetime by nearly 400 percent.

Brain Development and Ability

Long-term cannabis use that begins during adolescence has a negative effect on intellectual function, according to numerous studies. A study published in the proceedings of the National Academy of Sciences in August 2012 examined the effects of long-term marijuana use that began during users’ teenage years. Study participants who used marijuana heavily during their teens and adulthood on average showed an eight point decrease in IQ.

A study by doctors at Northwestern University and Harvard Medical School found that in young adults who use cannabis at least once a week, the size and shape of the two brain regions that affect motivation and emotion are different from those of their peers who do not consume the drug. This suggests that even light marijuana use can greatly affect the brain.

Other studies cited by theDrug Enforcement Administration suggest that adolescent marijuana use is linked to decreased ability to think, slower psychomotor speed, smaller attention span, and poorer memory.

About the Author:
Trey Dyer is a writer for and an advocate for substance use disorder treatment. When Trey is not writing, he can be found fly fishing, surfing, and enjoying time on the water in Florida.

For More Information:

An Evidence Based Review of Acute and Long-Term Effects of Cannabis Use on Executive Cognitive Functions. Crean, R., Crane, N.& Mason, B.

Potency trends of Δ9-THC and other cannabinoids in confiscated cannabis preparations from 1993 to 2008. Mehmedic, Z. et al..

National Institute on Drug Abuse. DrugFacts: Marijuana.

NIDA For Teens. .

The Dangers and Consequences of Marijuana Abuse. U.S.Department of Justice.

Adverse Health Effects of Marijuana Use.Volkow, N. et al.


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