Studies have found that using marijuana before age 18 is associated with shorter attention spans and lower IQ levels. Early use of marijuana has also been shown to correlate with changes in the structure of the teenage brain.
But that information hasn't exactly filtered down to teenagers.
"You always smell it," says "Pablo," a 15-year-old sophomore at a high school in Highland Park. "You always hear people talking about it. I think it's pretty common."
Two more sophomores at the high school, "Mary" and Betty," admit they use pot. And they like it. KPCC is not using any of the students' real names because it's illegal for teens to smoke pot.
"It makes you forget about all the bull that happens off in high school," Mary says. Betty adds, "You're in your own little world. No one can judge you and you can just be yourself. More than yourself — be all happy for once in your life."
Regulation and education could drive teen pot use down, advocates say
If voters approve Proposition 64, also known as the Adult Use of Marijuana Act, it will still be illegal for teenagers like Pablo, Mary and Betty to smoke. A big question for many people is whether teen pot use would increase if recreational marijuana were legal for adults.
Proposition 64 would prohibit the sale of non-medical marijuana to people younger than 21 years old. It also includes other safeguards intended to keep pot out of teenagers' hands: It prevents marijuana businesses from being located within 600 feet of schools, and it prevents pot products from being advertised to kids.
Advocates say these types of regulations, plus public education, could actually decrease teen pot use. That's what's happened with other substances, says Paul Armentano, deputy director for the National Organization for the Reform of Marijuana Laws.
"The use of alcohol and tobacco in this country are now at historic lows among young people," he says. "We can expect to see similar results in a regulated marketplace for marijuana as well."
Little data actually exists on whether teen pot use increases when recreational marijuana is legalized. It's now legal in four states and the District of Columbia, but experts say it's too soon to know if more teens are smoking in those places. It's been legal the longest in Colorado, but early data from there is contradictory.
The 2015 Healthy Kids Colorado Survey, conducted by the Colorado public health department, finds the percentage of teens who smoke pot hasn't really changed since legalization. Colorado's law took effect in December 2012. The year before, 22 percent of teens reported using pot in the past month. In 2015, 21 percent reported use in the past month.
Colorado's results are consistent with national data from the Centers for Disease Control and Prevention's Youth Risk Behavior Survey, which has been asking high school students about their drug and alcohol use for 25 years. It finds that in 2015, about 22 percent reported currently using pot.
Meanwhile, the federal National Survey on Drug Use and Health finds a 20 percent increase in teen pot use in the two years after legalization.
In the absence of complete data, advocates of legalization point to research concluding that teen pot use has not increased in states that have legalized medical marijuana.
These studies prove that, "when we have a regulated market, society has the ability to limit and control who provides marijuana legally, who distributes marijuana legally, and who uses marijuana legally, and where those individuals are allowed to use marijuana," says Paul Armentano, deputy director of the National Organization to Reform Marijuana Laws.
Would legalizing recreational pot change the message?
But comparing the effects of medical and recreational marijuana laws on teen pot use is like comparing apples and oranges, says Dr. Sarah Landsman, an assistant professor at the University of Florida.
"There's a big difference between patients trying to access a medication and an industry being developed that can be powerful and can have lobbyists, and can market a product," says Landsman, who authored one of the papers on the effects of medical marijuana laws on teens.
She adds that if recreational marijuana were legal, companies' goals, "won't be public health; their goal will be making a profit."
Dr. Bonnie Halpern-Felsher, a pediatrics professor at Stanford University, is also concerned that if marijuana were legal and widely marketed, teens would perceive it as a low-risk product.
Based on her research on marijuana, alcohol and tobacco, Halpern-Felsher says, "if adolescents perceive low risk and high benefit to any particular substance, then they are more likely to go on and use those products."
She says teens' perception that marijuana is harmless would only deepen with legalization.
"They're really going to think that marijuana is safer, regulated, and that it must be OK if the government is allowing us to use it," she says.
Mary, one of the teenage pot smokers at the Highland Park high school, agrees with Halpern-Felsher’s theory that if pot were legal for adults, more teens would smoke.
"People would finally see that weed isn't bad," Mary says.
The takeaway is this: If Californians vote in November to legalize recreational pot, it will probably take several years to determine how that will affect teen use. And the Golden State will be the largest laboratory yet to run this experiment.