Conference Coverage

AAP: Marijuana is harmful, addictive, and on the rise




Marijuana is dangerous, and you need to know how dangerous to adequately counsel adolescent patients and their families.

The growing number of states legalizing marijuana, whether exclusively for medical use or for recreational use, is changing the landscape for physicians, addiction specialists, and others working in public health, explained Dr. Miriam Schizer of the adolescent substance abuse program at Boston Children’s Hospital.

Currently, 23 states plus Washington have legalized medical marijuana, and 4 states plus Washington have legalized recreational use, Dr. Schizer said at the annual meeting of the American Academy of Pediatrics. Cannabis products are expanding rapidly, with many becoming more potent, but misconceptions about marijuana use also are potent and growing.

The proportion of high school seniors who believe marijuana carries a “great risk of harm” is nearly at an all-time low, based on findings from the Monitoring the Future survey. ©iStock/


The proportion of high school seniors who believe marijuana carries a “great risk of harm” is nearly at an all-time low, based on findings from the Monitoring the Future survey. With annual samples of approximately 50,000 8th, 10th and 12th grade students each year, the survey provides a glimpse into long-term trends in adolescents’ attitudes and behaviors regarding substance use. Just over a third of high school seniors (36%) perceived marijuana to have a great risk of harm in 2014, one of the lowest recorded numbers since the survey began in 1975. And 14% of seniors surveyed reported having used marijuana in the past month.

Understanding the mechanisms of THC

The primary psychoactive ingredient in marijuana is delta-9 tetrahydrocannabinol, or THC, one of more than 100 cannabinoids in marijuana. This fat-soluble molecule crosses both the blood-brain barrier and the placenta and accumulates in adipose tissue, where its half-life ranges from several days to a week. Its concentration in cannabis products also has increased from an average of less than 4% in 1994 to an average of 9% in cannabis products in 2008.

The way THC makes its way into adolescents’ systems varies: Smoking buds and leaves is the most common, but people also eat edible products, inhale cannabis through hookahs or e-cigarette–like “vaping” systems, or use hash oil “dabbing” for an exceptionally potent dose.

While the positive effects of cannabis use are what keep users coming back, the negative effects are just as common and can carry over until the day after, like a hangover. Those include paranoia, anxiety, irritability, impaired short-term memory, poor attention or judgment, poor coordination, distorted spatial perception, and an altered sense of the passage of time. The positive effects that users report include reduced anxiety, increased sociability, the perception that time slows down, an increased appetite, decreased pain, and overall euphoria.

Physiologic effects – peaking 30 minutes after inhalation or 2-4 hours after ingestion – can include tachycardia up to 20-50 beats per minute above baseline, increased blood pressure, bronchial relaxation, red eyes, and dry mouth and throat. These effects increase with the concentration of THC, also increasing the likelihood of paranoia, panic, hallucinations, vomiting, erratic mood swings, and aggressive behavior.

Following the discovery of cannabinoid receptors in the brain in 1988, scientists learned that the brain contains its own cannabinoid known as anandamide, giving rise to an endocannabinoid system in the brain. This system shapes brain development, supports myelin growth on neurons, and controls neuron activity. Both THC and anandamide play a role in regulating neurotransmitters such as dopamine, glutamate, endorphins, and serotonin, but THC has much stronger, longer-lasting effects and consequently interferes with cell function and growth.

Misconceptions about marijuana use

Dr. Schizer addressed the most common myths about marijuana use, pointing out that it is harmful to human health, it is addictive, and it does impair driving. Short-term harms include impaired short-term memory and motor coordination, altered judgment, and, in higher doses, paranoia and psychosis.

“There is a link to worsening depression and anxiety over time,” Dr. Schizer said. “Something is emerging very clearly: Among individuals with a genetic disposition to psychotic disorder, there’s an increased risk of developing the psychotic disorder.”

Long-term use can alter brain development, particularly among those using it in early adolescence, and lead to higher dropout rates, a lower IQ, and a poorer sense of life satisfaction. In one study of 1,037 individuals tracked from age 13 to 38 years, the average IQ of those who never used marijuana ranged from 99.8 to 100.6, compared with 99.7 to 93.9 among those dependent on marijuana for at least 3 years (Proc Natl Acad Sci USA. 2012 Oct 2;109[40]:E2657-64).

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