The number of marijuana users among teens is increasing. The Substance Abuse and Mental Health Services Administration reported in 2013:

[M]arijuana use rose to 7.5% of users aged 12 or older in 2013. This is up from 6.2% of users in 2002.

Additional NSDUH findings on marijuana include:

•          19.8 million (7.5%) people were current (past month) users of marijuana in 2013, making it the most used illicit drug.
•          Marijuana use was most prevalent among people age 18 to 25 (with 19.1% using it in the past month).
•          7.1% of people aged 12 to 17 reported using marijuana.
•          A higher percentage of males (9.7%) used marijuana in the past month than females (5.6%).

These numbers will not decrease when more states legalize the drug, because of the widespread availability.

Marijuana is not a harmless drug, as many of the people I talk to believe.

1. Risk of addiction

Not everyone who smokes marijuana will get addicted, but does a reasonable person want to risk it? A team of medical professionals published their study of cannabis in the New England Journal of Medicine (NEJM), concluding: “Despite some contentious discussions regarding the addictiveness of marijuana, the evidence clearly indicates that long-term marijuana use can lead to addiction.”

2. Risk of cardiovascular (heart) disease

Summarizing a French study, the LA Times reports:

"There is now compelling evidence on the growing risk of marijuana-associated adverse cardiovascular effects, especially in young people," said Emilie Jouanjus, lead author of the French study, which was also published in the Journal of the American Heart Assn. That evidence, Jouanjus added, should prompt cardiologists to consider marijuana use a potential cause of cardiovascular disease in patients they see.

(See also here.)

3. Risk of using harder drugs

Marijuana could be a gateway drug. The authors of the marijuana study reported in the NEJM say: “Epidemiologic and preclinical data suggest that the use of marijuana in adolescence could influence multiple addictive behaviors in adulthood.”

William J. Bennett and Robert A. White insightfully observe that not everyone who smokes marijuana will go on to a harder drug, but nearly everyone on a harder drug began with marijuana (p. 114)

4. Risk of lung damage

The American Lung Association reports:

Smoking marijuana clearly damages the human lung. Research shows that smoking marijuana causes chronic bronchitis and marijuana smoke has been shown to injure the cell linings of the large airways, which could explain why smoking marijuana leads to symptoms such as chronic cough, phlegm production, wheeze and acute bronchitis.

5. Risk of brain chemistry damage

A study by the Society of Nuclear Medicine and reported in Sciencedaily concludes:

Definitive proof of an adverse effect of chronic marijuana use revealed at SNM's 58th Annual Meeting could lead to potential drug treatments and aid other research involved in cannabinoid receptors, a neurotransmission system receiving a lot of attention. Scientists used molecular imaging to visualize changes in the brains of heavy marijuana smokers versus non-smokers and found that abuse of the drug led to a decreased number of cannabinoid CB1 receptors, which are involved in not just pleasure, appetite and pain tolerance but a host of other psychological and physiological functions of the body.

6. Risk of brain structure damage and memory loss

A study conducted by the Northwestern University Feinberg School of Medicine and reported in the Bulletin of Schizophrenia and a Northwestern news release concludes:

“The study links the chronic use of marijuana to these concerning brain abnormalities that appear to last for at least a few years after people stop using it,” said lead study author Matthew Smith, an assistant research professor in psychiatry and behavioral sciences at Northwestern University Feinberg School of Medicine. “With the movement to decriminalize marijuana, we need more research to understand its effect on the brain.”

It should also be noted in that excerpt that the authors of the study urge caution about decriminalizing marijuana.

7. Risk of schizophrenia

The same study by Northwestern University Feinberg School of Medicine observes:

Chronic use of marijuana may contribute to changes in brain structure that are associated with having schizophrenia, the Northwestern research shows. Of the 15 marijuana smokers who had schizophrenia in the study, 90 percent started heavily using the drug before they developed the mental disorder. Marijuana abuse has been linked to developing schizophrenia in prior research.

8. Risk of an IQ drop among adolescents

The lead IQ study investigator Madeline H. Meier says:

"Our results suggest that adolescents are particularly vulnerable to develop cognitive impairment from cannabis and that the drug, far from being harmless, as many teens and even adults are coming to believe, can have severe neurotoxic effects on the adolescent brain."

This study was attacked for not considering other factors, like socio-economic class. So a year later Dr. Nora Volkow of the National Institute of Drug Abuse says marijuana use is at least one contributory factor in the IQ drop:

“The message inherent in these and in multiple supporting studies is clear. Regular marijuana use in adolescence is known to be part of a cluster of behaviors that can produce enduring detrimental effects and alter the trajectory of a young person’s life -- thwarting his or her potential. Beyond potentially lowering IQ, teen marijuana use is linked to school dropout, other drug use, mental health problems, etc. Given the current number of regular marijuana users (about 1 in 15 high school seniors) and the possibility of this number increasing with marijuana legalization, we cannot afford to divert our focus from the central point: regular marijuana use stands to jeopardize a young person’s chances of success -- in school and in life.”

9. Risk of car crashes

Marijuana slows the motor or movement skills in users, so not surprisingly there is an increase in the incidents of car crashes. USA Today reports the findings:

As more states are poised to legalize medicinal marijuana, it's looking like dope is playing a larger role as a cause of fatal traffic accidents.

Columbia University researchers performing a toxicology examination of nearly 24,000 driving fatalities concluded that marijuana contributed to 12% of traffic deaths in 2010, tripled from a decade earlier.

NHTSA studies have found drugged driving to be particularly prevalent among younger motorists. One in eight high school seniors responding to a 2010 survey admitted to driving after smoking marijuana. Nearly a quarter of drivers killed in drug-related car crashes were younger than 25. Likewise, nearly half of fatally injured drivers who tested positive for marijuana were younger than 25.

Since legalizing marijuana, Colorado has seen an increase:

Colorado has seen a spike in driving fatalities in which marijuana alone was involved, according to Insurance.com. The trend started in 2009 -- the year medical marijuana dispensaries were effectively legalized at the state level.

10. Summary of the risks of altered behavior and diminished achievement

This last point summarizes the general health risks.

The American Academy of Child and Adolescent Psychiatry issued this statement:

Use of marijuana can lead to:

• School difficulties
• Problems with memory and concentration
• Increased aggression
• Car accidents
• Use of other drugs or alcohol
• Risky sexual behaviors
• Increased risk of suicide
• Increased risk of psychosis

Long-term use of marijuana can lead to:

• The same breathing problems as smoking cigarettes (coughing, wheezing, trouble
• with physical activity, and lung cancer)
• Decreased motivation or interest
• Lower intelligence
• Mental health problems, such as depression, anxiety, anger, moodiness, and
• psychosis
• Decreased or lack of response to mental health medication
• increased risk of side effects from mental health medication

Sometimes these studies are contested because they are supposedly sponsored by big corporations or skewed by political pressure put on government institutes. However, the marijuana legalization advocates are also motivated by politics and money. The more users they get, the more money flows their way. It’s a commercial enterprise.

So can we break the deadlock?

Common sense combined with science is just about all we got. Inhaling smoke of a chemical-laden and brain-tweaking drug defies both.

More importantly, behind these policy statements and scientific findings and hyperskepticism about motives and science are human lives.

Think before you take up this drug. Your quality of life will be negatively affected. If you currently take it, be persuadable and stop.

Given these health risks, states must no longer vote to legalize recreational marijuana -- and states that have legalized recreational use must reconsider and reverse their unwise decision.

James Arlandson, Ph.D. (1994), has taught college and university for years. His website is Live as Free People.