Medical marijuana legalization

Evidence Rating  
Evidence rating: Mixed Evidence

Strategies with this rating have been tested more than once and results are inconsistent or trend negative; further research is needed to confirm effects.

Health Factors  
Decision Makers
Date last updated

Policies that legalize marijuana for medical purposes remove civil or criminal penalties and permit the sale and use of medical marijuana products for eligible patients1, 2. Marijuana use is illegal in the United States at the federal level. Some states allow medical marijuana use for eligible patients; requirements and restrictions regarding patient authorization and registration, caregiver role and registration, medical conditions, home cultivation, and dispensary permission vary by state3.  

What could this strategy improve?

Expected Benefits

Our evidence rating is based on the likelihood of achieving these outcomes:

  • Improved health outcomes

  • Reduced substance abuse

  • Reduced alcohol-related harms

Potential Benefits

Our evidence rating is not based on these outcomes, but these benefits may also be possible:

  • Reduced illegal drug use

What does the research say about effectiveness?

There is mixed evidence about the health benefits and risks of legalizing marijuana for medical use.

Medical marijuana has been shown to reduce spasticity and chronic pain including neuropathic pain4, 5, 6, 7, 8, and treat nausea and vomiting for patients4. Studies of states with medical marijuana laws (MMLs) suggest legalization can reduce opioid overdose deaths9 and opioid abuse-related hospitalization10. MMLs that permit dispensaries also appear to be associated with decreases in opioid addiction and overdose deaths11.

However, legalizing marijuana for medical use can increase marijuana use and dependence among adults1, 12, 13, especially high-risk users (e.g., arrestees, heavy users, and multiple substance users)1. MMLs are associated with increased risk of unintentional toxic ingestions of medical marijuana products among children14, 15 and may increase youth initiation of marijuana use16. Additional evidence is needed to confirm effects on youth use overall1. Youth marijuana use may harm academic and employment outcomes, and social relationships4.         

Some studies suggest that MMLs may increase both marijuana and alcohol use. However, other studies suggest that MMLs may increase marijuana use but decrease alcohol use2.

Smoking marijuana may lead to respiratory problems, heart attacks, and cancers4, 17. Marijuana use may also increase the risk of psychotic and schizophrenic symptoms and may worsen schizophrenia, especially in genetically susceptible individuals and youth18, 19. Marijuana initiation before adulthood may increase the likelihood of dependence and related harms18, 19, 20; initiation over the age of 25 rarely results in dependence19

How could this strategy impact health disparities? This strategy is rated no impact on disparities likely.
Implementation Examples

As of August 2019, medical marijuana is legal in 33 states and Washington, D.C.; these states also have comprehensive medical marijuana and cannabis programs. Thirteen states allow limited use of low tetrahydrocannabinols (known as THC), high cannabidiol (CBD) products for specific medical conditions. Idaho and Kansas ban marijuana use3, 21.

As of October 2019, 11 states and Washington, D.C. allow residents to use marijuana for recreational use22.

Implementation Resources

NCSL-MMLs - National Conference of State Legislatures (NCSL). State medical marijuana laws (MMLs).

MPP - Marijuana policy project (MPP). We change laws.

LawAtlas-Marijuana - LawAtlas. Medical marijuana laws for patients map.


* Journal subscription may be required for access.

1 Pacula 2017 - Pacula RL, Smart R. Medical marijuana and marijuana legalization. Annual Review of Clinical Psychology. 2017;13(1):397-419.

2 Guttmannova 2016 - Guttmannova K, Lee CM, Kilmer JR, et al. Impacts of changing marijuana policies on alcohol use in the United States. Alcoholism: Clinical & Experimental Research. 2016;40(1):33-46.

3 NCSL-MMLs - National Conference of State Legislatures (NCSL). State medical marijuana laws (MMLs).

4 NASEM 2017 - National Academies of Sciences, Engineering, and Medicine (NASEM). The health effects of cannabis and cannabinoids: The current state of evidence and recommendations for research. Washington, D.C.: The National Academies Press; 2017.

5 Whiting 2015 - Whiting PF, Wolff RF, Deshpande S, et al. Cannabinoids for medical use: A systematic review and meta-analysis. JAMA. 2015;313(24):2456-2473.

6 Hill 2015 - Hill KP. Medical marijuana for treatment of chronic pain and other medical and psychiatric problems: A clinical review. JAMA. 2015;313(24):2474-2483.

7 Koppel 2014 - Koppel BS, Brust JCM, Fife T, et al. Systematic review: Efficacy and safety of medical marijuana in selected neurologic disorders: Report of the Guideline Development Subcommittee of the American Academy of Neurology. Neurology. 2014;82(17):1556-1563.

8 Cinti 2009 - Cinti S. Medical marijuana in HIV-positive patients: What do we know? Journal of the International Association Providers of AIDS Care. 2009;8(6):342-6.

9 Bachhuber 2014 - Bachhuber MA, Saloner B, Cunningham CO, Barry CL. Medical cannabis laws and opioid analgesic overdose mortality in the United States, 1999-2010. JAMA Internal Medicine. 2014;174(10):1668-1673.

10 Shi 2017 - Shi Y. Medical marijuana policies and hospitalizations related to marijuana and opioid pain reliever. Drug and Alcohol Dependence. 2017;173:144-150.

11 NBER-Powell 2015 - Powell D, Pacula RL, Jacobson M. Do Medical Marijuana Laws Reduce Addictions and Deaths Related to Pain Killers? National Bureau of Economic Research (NBER). 2015: Working Paper 21345.

12 Maxwell 2016 - Maxwell JC, Mendelson B. What do we know about the impact of the laws related to marijuana? Journal of Addiction Medicine. 2016;10(1):3-12.

13 Pacula 2015 - Pacula RL, Powell D, Heaton P, Sevigny EL. Assessing the effects of medical marijuana laws on marijuana use: The devil is in the details. Journal of Policy Analysis and Management. 2015;34(1):7-31.

14 Wang 2013a - Wang GS, Roosevelt G, Heard K. Pediatric marijuana exposures in a medical marijuana state. JAMA Pediatrics. 2013;167(7):630-633.

15 RAND-Pacula 2017 - Pacula RL. Regulating medical marijuana markets: Insights from scientific evaluations of state experiments. Santa Monica: RAND Corporation; 2017.

16 Wen 2015 - Wen H, Hockenberry JM, Cummings JR. The effect of medical marijuana laws on adolescent and adult use of marijuana, alcohol, and other substances. Journal of Health Economics. 2015;42:64-80.

17 Leung 2011 - Leung L. Cannabis and its derivatives: Review of medical use. Journal of the American Board of Family Medicine. 2011;24(4):452-62.

18 Caulkins 2012 - Caulkins JP, Hawken A, Kilmer B, Kleiman MAR. Marijuana legalization: What everyone needs to know. New York: Oxford University Press; 2012.

19 Bostwick 2012 - Bostwick JM. Blurred boundaries: The therapeutics and politics of medical marijuana. Mayo Clinic Proceedings. 2012;87(2):172-86.

20 Wilsey 2008 - Wilsey B, Marcotte T, Tsodikov A, et al. A randomized, placebo-controlled, crossover trial of cannabis cigarettes in neuropathic pain. Journal of Pain. 2008;9(6):506-21.

21 MPP - Marijuana policy project (MPP). We change laws.

22 NCSL-Marijuana - National Conference of State Legislatures (NCSL). Marijuana overview.