What Are the Risks of Marijuana Use?

Marijuana is classified as a Schedule 1 drug, which has made obtaining the drug for clinical research purposes extremely difficult. In August, the U.S. Drug Enforcement Agency announced a policy change to expand access to marijuana for research purposes. Research that has been done raises serious concerns about detrimental effects on individual and public health and safety: 

Addiction

  • Marijuana can cause the classic characteristics of an addictive substance, including craving, tolerance, dependence, continued use despite adverse effects on one’s life, and withdrawal symptoms. Withdrawal symptoms can include irritability, sleeping difficulties, dysphoria, craving, and anxiety.
  • In the United States, marijuana is the third most common cause of drug dependence after tobacco and alcohol.2  
  • Nine percent of those who try marijuana will become addicted. For those who start using as teenagers, this increases to approximately 17%, and for those who use marijuana daily, the rate of addiction is as high as 25 to 50%.

Cognitive Impairment and Adolescent Brain Development

  • Adolescents who engage in low to moderate marijuana use experience an increase in observable attention and academic problems when using marijuana at least monthly.4
  • Those under age 15 who use cannabis are at increased risk for dropping out of school, and for dissatisfaction with their lives and relationships.5  
  • Academic performance in adolescents suffers with marijuana use, and is weakest among those using marijuana at least weekly.6
  • Marijuana use has been associated with memory impairment; higher levels of use are correlated with worse outcomes on verbal memory testing in middle age.7
  • Young adults who chronically smoke marijuana showed a loss of brain gray matter, which is responsible for motivation, emotional state, and affective processing.

Increase in Motor Vehicle Accidents

  • The use of marijuana increases the risk of motor vehicle accidents.9
  • The risk for fatal crashes increases, most markedly among those aged 16–20, when alcohol is combined with other drugs, including marijuana.10

Risk During Pregnancy

  • The fetuses of mothers who smoked cannabis experience growth restriction, reduced head circumference, and lower birth weight in mid- and late pregnancy compared to non-exposed fetuses.11
  • Cannabis mothers had statistically higher rates of spontaneous preterm births.12

Reports of Adverse Public Health Outcomes following Legalization of Recreational Marijuana in Other States

States that have legalized recreational marijuana have seen troubling public health effects:

Youth Access to Marijuana

  • The number of children under 10 seen at one Colorado children’s hospital for marijuana exposure almost doubled in the two years year before and after legalization. The median age was 2.4 years.13
  • After recreational marijuana legalization, 11.16% of Colorado youth ages 12 to 17 years old were considered current marijuana users compared to 7.15% nationally. Colorado ranked third in the nation and was 56% higher than the national average.14  
  • Drug-related suspensions/expulsions from schools increased 40% from 2008-2009 to 2013-2014, after recreational marijuana legalization in Colorado. The vast majority were for marijuana violations.18 
  • Youth aged 12 to 17 years old who had used marijuana in the past month increased 20% in the two year average following legalization of recreational marijuana in Colorado, compared to the two‐year average prior to legalization. Nationally, youth past month marijuana use decreased 4% during the same timeframe.15

Edibles  

  • Colorado saw an increase in hospital emergency room visits by children, adolescents and adults following intentional or accidental exposure to edibles.16    

ER Visits

  • After recreational marijuana legalization in Colorado, the number of marijuana-related emergency room visits increased 29%, and marijuana-related hospitalizations increased 38%, in only one year.19 

Motor Vehicle Accidents

  • Marijuana‐related traffic deaths increased an average of 48% in the three years following legalization of recreational marijuana compared to the three years prior to legalization. All traffic deaths increased 11% during the same time period.17
  • Washington drivers with active THC in their blood involved in fatal driving accidents increased 122.2% from 2010 to 2014.18 
  • Approximately 20% of all traffic deaths in Colorado in 2014 were marijuana-related, compared to 10% before recreational marijuana legalization.19

The Massachusetts Special Senate Committee on Marijuana, following a fact-finding visit to Colorado, and a thorough review of lessons learned from other states that have legalized marijuana, noted the following concerns about legalizing recreational marijuana: 

  • Youth access, and youth perception that marijuana is safe, increases, even with strong safeguards in place
  • Edibles, which are the fastest growing segment of the marijuana market, are particularly challenging for public health and safety.
  • The high potency of today’s marijuana products increases the risk of harmful health consequences and addiction
  • The black market for marijuana is likely to continue after legalization
  • Tax revenues and fees may fall short of even covering the full public and social costs, including regulation, enforcement, public health and safety, and substance abuse treatment


  1. Volkow ND, et al. Adverse Effects of Marijuana Use. N Engl J Med. 370;23 2219-27
  2. Hall W, et al. Adverse health effects of non-medical cannabis use. Lancet. 2009 Oct 17;374(9698):1383-91
  3. Volkow ND, et al. Adverse Effects of Marijuana Use. N Engl J Med. 2014 370;23 2219-27
  4. Pardini D, et al. Unfazed or Dazed and Confused: Does Early Adolescent Marijuana Use Cause Sustained Impairments in Attention and Academic Functioning? J Abnorm Child Psychol 2015 43:1203–1217
  5. Hall W, et al. Adverse health effects of non-medical cannabis use. Lancet. 2009;374: 1383–9
  6. Stiby AI, et al. Adolescent cannabis and tobacco use and educational outcomes at age 16: birth cohort study. Addiction. 2015 110, 658–668
  7. Auer R, et al. Association between Lifetime Marijuana Use and Cognitive Function in Middle Age: The Coronary Artery Risk Development in Young Adults (CARDIA) Study. JAMA Internal Medicine online February 01, 2016
  8. Battistella G, et al. Long-term effects of cannabis on brain structure. Neuropsychopharmacology (2014) 39, 2041–2048
  9. Asbridge M, et al. Acute cannabis consumption and motor vehicle collision risk: systematic review of observational studies and meta-analysis. BMJ 2012;344:e536
  10. Romano E, et al. Drugs and Alcohol: Their Relative Crash Risk. Journal of Studies on Alcohol and Drugs. Jan 2014. 56-64
  11. El Marroun H, et al. Intrauterine cannabis exposure affects fetal growth trajectories: the Generation R Study. J Am Acad Child Adolesc Psychiatry. 2009 Dec;48(12):1173-81
  12. Saurel-Cubizolles MJ, et al. Cannabis use during pregnancy in France in 2010. BJOG. 2014 Jul;121(8):971-7
  13. Wang G., et al. Unintentional Pediatric Exposures to Marijuana in Colorado, 2009-2015 J Pediatr. Published online July 25, 2016.
  14. Rocky Mountain High Intensity Drug Trafficking Area (RMHIDTA) Investigative Support Center, “The Legalization of Marijuana in Colorado: The Impact,” Volume 3, September 2015.
  15. Rocky Mountain High Intensity Drug Trafficking Area (RMHIDTA) Investigative Support Center, “The Legalization of Marijuana in Colorado: The Impact,” Volume 4, September 2016.
  16. Rocky Mountain High Intensity Drug Trafficking Area (RMHIDTA) Investigative Support Center, “The Legalization of Marijuana in Colorado: The Impact,” Volume 2, August 2014.
  17. Rocky Mountain High Intensity Drug Trafficking Area (RMHIDTA) Investigative Support Center, “The Legalization of Marijuana in Colorado: The Impact,” Volume 4, September 2016.
  18. Washington Traffic Safety Commission, “Driver Toxicology Testing and the Involvement of Marijuana in Fatal Crashes, 2010-2014”, February 2016..
  19. Rocky Mountain High Intensity Drug Trafficking Area (RMHIDTA) Investigative Support Center, “The Legalization of Marijuana in Colorado: The Impact,” Volume 4, September 2016.








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