How accurate are the Surgeon General’s claims on marijuana?

By John Murphy, MDLinx
Published September 9, 2019

Key Takeaways

The US Surgeon General held a news conference on August 29 where he warned Americans about the harms of marijuana on infants and teenagers.

“Recent increases in access to marijuana and in its potency, along with misperceptions of its safety, endanger our most precious resource, our nation’s youth,” stated Surgeon General Jerome M. Adams, MD, MPH.

“No amount of marijuana use during pregnancy or adolescence is known to be safe,” he said emphatically.

He also pointed out that the cannabis produced now is far more potent than that of yesteryear.

The amount of tetrahydrocannabinol (THC), “the component responsible for euphoria and intoxication, but also for most of marijuana’s documented harms, has increased three- to five-fold over the last few decades. And that’s before you take into account concentrated forms such as edibles, oils, and waxes that can increase THC delivery even further, by as much as an additional three-fold,” Dr. Adams explained.

“Or, as I like to say, this ain’t your mother's marijuana,” he added.

Let’s take a closer look at the research behind the Surgeon General’s recent advisory.

Are more teens using more pot?

The Surgeon General stated that, as more states have permitted the legalization of marijuana, perceptions about its risks and harms have declined among high school students in the past few years.

“Marijuana is now the third most commonly used illicit substance in adolescents, behind alcohol and e-cigarettes,” Dr. Adams said. “In 2017, new marijuana users between the ages 18 and 25 rose by almost 30%, and more than 9 million 12- to 25-year-olds reported marijuana use in the prior month.”

The Surgeon General’s implication is clear: Teenagers are smoking more pot.

But a good deal of evidence shows it’s just the opposite: Teenagers appear to be using cannabis less. The most compelling study on this comes from a federal agency—the Substance Abuse and Mental Health Services Administration—which showed that cannabis use among teenagers has been on a slow decline for more than a decade.

Legalization may even encourage a decline in marijuana use among teenagers, according to the authors of a recent JAMA Pediatrics article.

Nevertheless, marijuana use among teenagers is still a major concern. About 1 in 16 high school seniors continue to use marijuana on a daily basis, despite that it’s illegal for them to do so.

Does weed make teens stupid?

The Surgeon General stated that frequent marijuana use during adolescence can impair attention, memory, and decision-making.

“Science tells us that young people who regularly use marijuana are more likely to show a decline in IQ and school performance, [and] are more apt to miss classes and ultimately drop out,” Dr. Adams said.

Not all scientists agree with that conclusion, though. Authors of a meta-analysis in JAMA Pediatrics point out that cannabis intoxication may result in acute cognitive deficits, but it’s not clear whether cannabis results in long-term cognitive effects that persist after acute intoxication, particularly after ceasing its use.

The authors concluded: “[O]ur analyses suggest a detectable but limited association between cannabis use and cognitive functioning in adolescents and young adults; for a majority of individuals, such effects may be of questionable clinical significance, especially after sustained abstinence.”

These findings concur with a report from The National Academies of Sciences, Engineering, and Medicine, which identified a number of confounders found in many studies. The authors of this report concluded that there is limited evidence of a statistical association between cannabis use and impaired academic achievement and education outcomes.

It’s important to note, however, that the findings from these meta-analyses disagree with those from a large, prospective, longitudinal study as well as a systematic review on long-term effects of cannabis use in abstinent adolescents and adults.

So, until additional long-term trials confirm or deny these conclusions, the jury is still out on whether (or to what extent) the teenage brain is lastingly impaired by cannabis.

Does cannabis affect babies’ development?

Because some pregnant women use marijuana to prevent or reduce morning sickness, the Surgeon General also took to task mothers who use marijuana while pregnant or nursing.

“In pregnant women, marijuana is now actually the most commonly used illicit drug. Between 2002 and 2017, marijuana use among pregnant women doubled,” Dr. Adams said.

He added: “Marijuana use during pregnancy can affect the baby’s brain, and also result in lower birth weight, a marker for early death and disability. THC is transmitted via breast milk, which is why [the American College of Obstetricians and Gynecologists] recommends against marijuana even after delivery.”

Experts agree that marijuana use during pregnancy is not advisable; however, evidence on the topic is still lacking.

“I don’t think the Surgeon General’s advisory says that we know everything and therefore we don’t need any more research,” said Susan Weiss, PhD, director of extramural research at the National Institute on Drug Abuse (NIDA), in an interview.  

To that end, NIDA provided a research grant to radiologists at the University of Washington School of Medicine, Seattle, WA, to study marijuana’s effects in pregnant women and their infants.

Said study investigator Natalia Kleinhans, PhD: “The very few investigations that have studied prenatal cannabis exposure and infant brain development have all involved women who are polysubstance drug users. No one has looked at marijuana use exclusively.”

Pregnant women recruited for the study will not be permitted to use alcohol, tobacco, and other drugs.

“This study is targeting a very specific population of women who are using marijuana to manage their symptoms while they’re pregnant,” Dr. Kleinhans said. “There’s little research to back up the medical and public health advice they’re getting to stay away from pot to control nausea.”

Marijuana is still a drug

This is not to say that it’s OK for teenagers and pregnant women to use marijuana—but it’s worth noting that much of the knowledge about marijuana use is still emerging.

Still, the Surgeon General does make a good point: More Americans are using marijuana without being aware of all its harms. For instance, the number of pregnant women who report using marijuana is going up, not down.

Even more striking, more than one-third of cannabis users don’t believe or don’t know that marijuana can be addictive. What they may not know is that marijuana addiction (more formally termed “marijuana use disorder”) occurs in about 30% of marijuana users.

“Nearly one in five people who begin marijuana use during adolescence become addicted,” the Surgeon General warned. “You can become addicted to marijuana.”

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