Marijuana and Teens: Know the Facts

shutterstock_198368684There is good news for parents concerned about drug use. The latest Monitoring the Future survey by the University of Michigan and the National Institute on Drug Abuse polled 45,473 students (eighth, 10th and 12th graders) from 372 schools on a variety of substance-use areas.

The report shows an overall decline in alcohol use, and the same goes for cigarettes, heroin, methamphetamines and prescription opioids. That’s encouraging.

One area that shows continued steady usage is marijuana. Of 12th graders, 35.6 percent report using it in the past year, and 22.5 percent in the past month. Also of note are teenagers’ attitudes toward the drug: 68.9 percent of 12th graders said that they don’t consider marijuana to be harmful. Though the same number of teens say they don’t approve of smoking it regularly, the numbers suggest a relatively relaxed mindset about the drug. 

Teen confusion about marijuana is understandable. There are mixed signals about it as some states have legalized the drug for adults (it’s still illegal for those under 21 in those states). So while parents may be heartened by the study’s overall results, it’s important to stay aware and communicative with teens about drug use. The same attitude is held by the NIDA, as shown by a statement by Nora D. Volkow, director of the association:

“Clearly our public health prevention efforts, as well as policy changes to reduce availability, are working to reduce teen drug use, especially among eighth graders. However, when 6 percent of high school seniors are using marijuana daily, and new synthetics are continually flooding the illegal marketplace, we cannot be complacent. We also need to learn more about how teens interact with each other in this social media era, and how those behaviors affect substance use rates.”

Here’s a look at some indications of marijuana use and the effects that can come from it.

Looking for signs

There are several ways that parents can detect marijuana usage, both in visual changes and attitude shifts. Here are a few of those, as detailed by the NIDA.

  • Hygiene: If teenagers suddenly stop bathing regularly, or brushing their teeth, this could be an indication of marijuana use.
  • The eyes: Marijuana use can cause bloodshot eyes, and teens may use eye drops to try to counter this.
  • Mood changes: Teenagers will naturally have mood swings, but a consistently negative or apathetic mood could be a clue to drug use.
  • Academics: Skipping school is a red flag, as is a sudden lack of interest and declining grades.
  • Friends: Teens that quickly gravitate from an established circle of friends to a new one may be experimenting with marijuana or other drugs.
  • Paraphernalia: Any sighting of rolling papers, a pipe or other smoking devices is a huge red flag. Anything that could be used to mask the smell of marijuana, like incense or candles, could be a clue as well.


What parents may have encountered with marijuana in their youth is likely quite different from current-day teenagers. Marijuana can be a much more powerful drug, which makes experimenting with it that much more risky. This is due to a spike in THC, defined by the NIDA as the chemical “responsible for many of the drug’s psychotropic (mind-altering) effects.”

“In the early 1990s, the average THC content in marijuana was about 3.74 percent,” the association reports. “In 2013, it was almost 10 percent, and much higher in some products such as oils and other extracts. Scientists do not yet know what this increase in potency means for a person’s health. It may cause users to take in higher amounts of THC — which could lead to greater health risks including increased risk of addiction, or they may adjust how they consume marijuana (by smoking or eating less) to compensate for the greater potency.”

Even higher levels of THC were reported in a 2015 CBS News story. Andy LaFrate of the American Chemical Society said in the story, “I would say the average potency of marijuana has probably increased by a factor of at least three. We’re looking at average potencies right now of around 20 percent THC.”


Marijuana has a direct effect on the brain, and there are complicated ways that a teenager’s behavior can be altered. Because the human brain isn’t fully formed until we are in our early-to-mid 20s, the introduction of marijuana can cause damaging effects. “It’s the absolute worst time,” says Krista Lisdahl of the University of Wisconsin, Milwaukee, in an NPR story written by Patti Neighmond. The teenage years, Lisdahl says, are the “last golden opportunity to make the brain as healthy and smart as possible.”

The basic elements of learning can be marred by marijuana. The NIDA describes its effect on the hippocampus, a part of the brain that “plays a critical role in certain types of learning.” Marijuana can disrupt the hippocampus’ functions, which “can lead to problems studying, learning new things, and recalling recent events. A recent study followed people from age 13 to 38 and found that those who used marijuana a lot in their teens had up to an 8 point drop in IQ, even if they quit in adulthood.”

And judgment can be impaired by marijuana, which can lead a teenager to dangerous scenarios. As the NIDA states: “Since THC affects areas of the frontal cortex involved in decision making, using it can cause you to do things you might not do when you are not under the influence of drugs — such as engaging in risky sexual behavior, which can lead to sexually transmitted diseases (STDs) like HIV, the virus that causes AIDS — or getting in a car with someone who’s been drinking or is high on marijuana.”

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