Study after study has concluded that marijuana policy reform is not linked to increased rates of marijuana use among teens. In July 2019, the Journal of the American Medical Association published a major report analyzing federal data from more than 1.4 million high school students.¹ The researchers found that legalization of marijuana for adults was associated with an 8% decline in past 30-day marijuana use and a 9% decline in frequent use among teens. The study also looked at medical cannabis laws and concluded they had no impact on youth marijuana use. These findings were consistent with the results of a meta-analysis of 55 academic papers and multiple data sources published by the journal Current Addiction Reports in September 2018. Those researchers wrote that, “Liberal forms of medical cannabis regulation … have not to date increased rates of cannabis use among adolescents.”²

Another major report focused on cannabis use disorders among adolescents from 2002 to 2013. During that time, as dozens of significant marijuana policy reforms were passed throughout the states, a peer-reviewed study in the Journal of the American Academy of Child & Adolescent Psychiatry found that, “Past-year prevalence of marijuana use disorders among US adolescents declined by an estimated 24%.”³

In 2012, Colorado and Washington became the first states to legalize marijuana for adult use. Both have conducted large-scale surveys involving tens of thousands of high school students in the years since. In each case, the results (see below) show an overall reduction in past 30-day marijuana use among teens. Research published in the journal Substance Abuse also suggests that legalization has not increased use among teens who were already using marijuana. 

As of August 2020, the available data suggests that regulating marijuana for adults’ use does not impact marijuana use among youth. Below are data tables for youth surveys comparing past 30-day marijuana use for teens before and after adult-use legalization laws passed in 10 states — Colorado, Washington, Oregon, Alaska, California, Maine, Massachusetts, Nevada, Vermont, and Michigan.⁴ In five of the states, government surveys indicate a slight decrease in teens’ marijuana use rates, while in the other half, surveys suggest a slight increase. In most cases, the changes were within the confidence intervals. Taken as a whole, rates are unchanged. Meanwhile, two nationwide surveys show a modest decrease in teen use since states began legalizing cannabis for adults.

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Washington State Healthy Youth Survey (past 30-day use) — Law enacted in November 2012 ⁵

	2010	2012	2014	2016	2018
8th grade	9.5%	9.4%	7.3%	6.4%	7.0%
10th grade	20.0%	19.3%	18.1%	17.2%	17.9%
12th grade	26.3%	26.7%	26.7%	26.4%	26.2%

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Colorado Healthy Kids Survey (past 30-day use) — Law enacted in November 2012 ⁶

	2011	2013	2015	2017
9th – 12th grade	22.0%	19.7%	21.2%	19.4%

 

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Oregon Healthy Teens Survey (past 30-day use) — Law enacted in November 2014 ⁷

	2013	2015	2017	2019
8th grade	9.7%	8.8%	6.7%	7.8%
11th grade	20.9%	19.1%	20.9%	20.4%

 

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Alaska Youth Risk Behavior Survey (past 30-day use) — Law enacted in November 2014 ⁸

	2013	2015	2017	2019
9th – 12th grade	19.7%	19.0%	21.5%	21.5%

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California Youth Risk Behavior Survey (past 30-day use) — Law enacted in November 2016 ⁹

	2015	2017	2019
9th – 12th grade	22.9%	21.8%	17.1%

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Massachusetts Youth Risk Behavior Survey (past 30-day use) — Law enacted in November 2016 ¹⁰

	2015	2017	2019
9th – 12th grade	24.5%	24.1%	26.0%

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Maine Youth Risk Behavior Survey (past 30-day use) — Law enacted in November 2016 ¹¹

	2015	2017	2019
9th – 12th grade	19.9%	18.8%	22.3%

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Nevada Youth Risk Behavior Survey (past 30-day use) — Law enacted in November 2016 ¹²

	2015	2017	2019
9th – 12th grade	19.3%	17.9%	19.8%

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Vermont Youth Risk Behavior Survey (past 30-day use) — Law enacted in January 2018 ¹³

	2017	2019
9th – 12th grade	23.5%	26.5%

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Michigan Youth Risk Behavior Survey (past 30-day use) — Law enacted in November 2018 ¹⁴

	2017	2019
9th – 12th grade	23.7%	26.5%

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National Survey on Drug Use and Health (past 30-day use, small sample size) ¹⁵

	‘12-’13	‘13-’14	’14-‘15	‘15-’16	‘16-’17	‘17-’18
U.S., 12-17 years old	7.2%	7.2%	7.2%	6.8%	6.5%	6.6%
Colo., 12-17 years old	11.2%	12.6%	11.1%	9.1%	9.0%	9.4%
Wash., 12-17 years old	9.8%	10.1%	9.2%	7.9%	9.0%	9.9%
Alaska, 12-17 years old	8.7%	9.2%	10.6%	10.4%	8.8%	7.9%
Ore., 12-17 years old	9.6%	10.2%	9.4%	9.8%	10.4%	9.7%
D.C., 12-17 years old	9.9%	10.6%	8.9%	8.1%	8.3%	8.5%
Nev., 12-17 years old	8.3%	8.0%	7.4%	8.7%	8.8%	9.2%
Maine, 12-17 years old	9.3%	9.9%	10.0%	9.7%	9.9%	10.3%
Calif., 12-17 years old	7.8%	8.7%	8.3%	7.3%	6.9%	7.1%
Mass., 12-17 years old	8.9%	8.9%	9.2%	8.7%	8.9%	9.3%

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Nationwide Youth Risk Behavior Survey (past 30-day use) ¹⁶

	2011	2013	2015	2017	2019
9th – 12th grade	23.1%	23.4%	21.7%	19.8%	21.7%

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¹ Anderson, Mark D., et al.. “Association of Marijuana Laws With Teen Marijuana Use New Estimates From the Youth Risk Behavior Surveys,” Journal of the American Medical Association, July 2019.
² Leung, Janni, et al. “Has the Legalisation of Medical and Recreational Cannabis Use in the USA Affected the Prevalence of Cannabis Use and Cannabis Use Disorders?,” Current Addiction Reports, September 2018.
³ Grucza, Richard A., et al. “Declining Prevalence of Marijuana Use Disorders Among Adolescents in the United States, 2002 to 2013.” Journal of the American Academy of Child & Adolescent Psychiatry, vol. 55, no. 6, 2016.
⁴ Illinois, which legalized marijuana for adults in 2019, does not have “after” data yet and is thus excluded.
⁵ Accessed here: http://www.askhys.net/FactSheets
⁶ Accessed here: https://www.colorado.gov/pacific/cdphe/hkcs
⁷ Accessed here: https://www.oregon.gov/oha/PH/BirthDeathCertificates/Surveys/OregonHealthyTeens/Pages/index.aspx
⁸ Accessed here: https://www.cdc.gov/healthyyouth/data/yrbs/results.htm
⁹ Ibid. 
¹⁰ Ibid.
¹¹ Ibid.
¹² Ibid.
¹³ Ibid.
¹⁴ Ibid.
¹⁵ Accessed here: https://www.samhsa.gov/data/data-we-collect/nsduh-national-survey-drug-use-and-health
¹⁶ Accessed here: https://nccd.cdc.gov/youthonline/App/Results.aspx?


Note: Other than the above surveys, the only data we are aware of is Monitoring the Future (MTF) surveys. However, MTF’s state-specific data is not publicly available. One study discussed MTF data and combined three years of “before” and three years of “after” data for two states. Unfortunately, MPP is unable to access the data necessary for a before-and-after comparison — comparing the year immediately preceding legalization with the most recent year for all states. MTF surveys also rely on a far smaller sample size for each state than the state-specific surveys. For example, Washington State’s HYS surveys more than 200,000 Washington students each year, while MTF surveyed only 5,509 students in Washington.