The chart below shows the official number of medical marijuana patients holding identification cards in the states (and District of Columbia) with mandatory registration. California and Washington have voluntary registration, so the patient numbers used are an estimate based on nearby states with mandatory registration. We listed three states (ND, OH, WV) that have legalized medical marijuana but for which no patient numbers are available yet. Those states were not included in our calculations to determine the total and average number of medical marijuana users.
We recognize the possibility that not all medical marijuana users register for identification cards and that not all of the people registered have valid medical uses for the marijuana.
State population numbers are estimates from the US Census Bureau's 2017 data. We looked at state medical marijuana program websites and emailed state officials to update the medical marijuana patient numbers in May 2018; all sources are listed below. Reference our Mar. 2016 and Oct. 2014 estimates to see how the numbers have changed.
Our national estimate of 3,514,510 medical marijuana users may not be nor is it intended to be scientifically or statistically sound. It is a rough estimate presented only to give a general reference point for discussion of medical marijuana use in the United States. 
How Many Legal Medical Marijuana Patients Are There in the United States?
Legal Medical Marijuana Patients: total medical marijuana users in 26 (out of 29) states and DC with legal medical marijuana (as of May 17, 2018)
Estimated number of users if medical marijuana were legal throughout all 50 US states and DC (based on avg. of 10.79 patients per 1,000)8
(2017 US population)
1. Arkansas has started issuing medical marijuana registry ID cards, but marijuana is not yet available in the state.
2. California had 5,848 registered patients in Fiscal Year 2017/2018, but registration is voluntary and most patients are not registered. We made an estimate using the per capita number of patients in Arizona because of geographical proximity. The Marijuana Policy Project's (MPP) Feb. 2018 estimate for California, 1,256,550, used Maine's per capita number of patients.
3. In presenting the number of medical marijuana registration cards printed, Maine's medical marijuana program website states, "This number is not an accurate reflection of the number of patients as it contains all certifications printed, including misprints, reissue of lost certifications and other anomalies."
4. The Division of Medical Marijuana in the North Dakota Department of Health wrote in a May 16, 2018 email to ProCon.org: "[W]e have not begun the patient process yet. We are in the process of determining the grow facilities. Once those are chosen we will have better time estimates on when the patient process will begin."
5. Ohio's medical marijuana program website states (as of May 16, 2018), "The only valid state ID cards will be issued by the State of Ohio Board of Pharmacy once the state's patient registry becomes available no later than September 2018."
6. Washington listed 32,123 recognition cards created as of May 16, 2018, but registration isn't required to be a medical marijuana patient except for patients under 18. As a result, we created an estimate based on the per capita patient numbers in Oregon.
7. West Virginia's Medical Cannabis Program website states (as of May 16, 2018), "Under the Act, the Bureau may not issue the patient and caregiver identification cards necessary to obtain medical cannabis until July 1, 2019."
8. If the average number of medical marijuana patients per 1,000 residents in states with legal medical marijuana is extrapolated to all 50 states (population 325,719,178 in 2017, according to the US Census Bureau), then the total number of medical marijuana users as of May 16, 2018 would theoretically be 3,514,510 [10.79/1,000 x 325,719,178 = 3,514,510].
9. Jeff Dang, PhD, Director of Statistics and Quality Analysis at FAIR Health Inc., commented on our methodology in a Mar. 10, 2009 email to ProCon.org. Although Mr. Dang's statement is based on our 2009 patient estimate of 577,712, the method we used in 2018 to estimate patients is the same.
"ProCon.org should be congratulated for providing an estimate of the number of people who hold identification cards for medical marijuana in several states throughout the country. Furthermore, ProCon.org has provided an estimate that currently serves as a general reference point for enumerating the total number of medical marijuana patients in the country. ProCon.org has conscientiously disclosed many of the problems associated with their estimates and provided the algorithms that were used to derive the estimates (see [above] footnotes). However, two notable limitations should be added and have been delineated below.
First, the current estimate of 577,712 included data from a variety of sources (e.g. estimates from the Marijuana Policy Project and data from the Census Bureau). In several states, different data collection and estimation methods were employed. It is important to note that each approach contributes additional sources of bias and error that have not been teased apart or accounted for in the current estimate. More generally, the quality of the data have not been verified or described in detail. Secondly, it is clear that systematic probability sampling techniques were not employed therefore these numbers cannot be generalized to the rest of the nation. In other words, these particular states are not representative of all states in the US and the sample data are not representative of US population.
To derive more accurate estimates, rigorous research methods should be employed. In particular, random sampling remains the gold standard for estimating prevalence. The reality, however, is that research is often conducted on a shoestring budget and practical concerns often prevent the kind of research that is actually desired."
Alaska: Alaska Department of Health and Social Services, "Alaska Facts & Figures: Medical Marijuana Cardholders by Year and Sex (2013-2017)," dhss.alaska.gov, Dec. 11, 2017
Arizona: Arizona Department of Health Services, "Arizona Medical Marijuana Program March 2018 Monthly Report," azdhs.com, Apr. 27, 2018
California: California Department of Public Health, "Patient, Primary Caregiver, Medi-Cal and CMSP Card Data," cdph.ca.gov, May 2, 2018 (registered); Marijuana Policy Project, "Medical Marijuana Patient Numbers," mpp.org, Feb. 26, 2018 (estimate)
Colorado: Colorado Department of Public Health & Environment, "Medical Marijuana Registry Program Statistics April 2018," www.colorado.gov, Apr. 2018
Connecticut: Connecticut State Department of Consumer Protection, "Medical Marijuana Statistics," ct.gov, May 13, 2018
Washington, DC: DC Health, "Medical Marijuana and Integrative Therapy Update," dchealth.dc.gov, Apr. 24, 2018
Delaware: Medical Marijuana Act Oversight Committee, "Delaware Medical Marijuana Program Annual Report," dhss.delaware.gov, Sep. 2017
Florida: Florida Department of Health Office of Medical Marijuana Use, "Weekly Update - May 11, 2018," floridahealth.gov, May 11, 2018
Hawaii: State of Hawaii, Department of Health Medical Cannabis Registry Program, "Program Statistics," health.hawaii.gov (accessed May 15, 2018)
Illinois: Illinois Department of Public Health, "Annual Progress Report: Compassionate Use of Medical Cannabis Pilot Program Act," dph.illinois.gov, Sep. 2017
Maine: Maine Center for Disease Control and Prevention, "Maine Medical Use of Marijuana Program January 1, 2016 - December 31, 2016: Annual Report to the Maine State Legislature," maine.gov, Apr. 21, 2017 (number of cards printed); Marijuana Policy Project, "Medical Marijuana Patient Numbers," mpp.org, Feb. 26, 2018 (estimate)
Maryland: Natalie M. LaPrade Maryland Medical Cannabis Commission, Email to ProCon.org, May 16, 2018
Massachusetts: Medical Use of Marijuana Program, "Massachusetts Medical Use of Marijuana Program Snapshot," mass.gov (accessed May 15, 2018)
Michigan: Andrew Brisbo, "Medical Marihuana Act Statistical Report with Program Information and Financial Data for Fiscal Year 2017," michigan.gov, Nov. 28, 2017
Minnesota: Minnesota Department of Health, "Medical Cannabis Program Update," health.state.mn.us, Apr. 2018
Montana: Montana Department of Health and Human Services, "Montana Marijuana Program (MMP) March 2018 Registry Information," dphhs.mt.gov, Mar. 2018
Nevada: Nevada Division of Public and Behavioral Health (DPBH), "Medical Marijuana Program Statistics," dpbh.nv.gov, Jan. 2016
New Hampshire: New Hampshire Department of Health and Human Services, "Therapeutic Cannabis Program 2017 Data Report," dhhs.nh.gov, Dec. 22, 2017
New Jersey: New Jersey Department of Health, "Murphy Administration Announces NJ Medicinal Marijuana Program Now Serving 20,000 Patients," nj.gov, May 1, 2018
New Mexico: New Mexico Department of Health, "Medical Cannabis Program April 2018 Patient Statistics," nmhealth.org, Apr. 2018
New York: New York Department of Health, "The New York State Medical Marijuana Program," health.ny.gov (accessed May 15, 2018)
North Dakota: North Dakota Department of Health Division of Medical Marijuana, Email to ProCon.org, May 16, 2018
Ohio: Ohio Medical Marijuana Control Program, "Ohio's Official Resource for the Medical Marijuana Control Program," medicalmarijuana.ohio.gov (accessed May 17, 2018)
Oregon: Oregon Medical Marijuana Program, "Oregon Medical Marijuana Program Statistical Snapshot April, 2018," oregon.gov, Apr. 6, 2018
Pennsylvania: Pennsylvania Department of Health, "Wolf Administration Approves Eight Universities as Certified Medical Marijuana Academic Clinical Research Centers," governor.pa.gov, May 14, 2018
Rhode Island: Rhode Island Department of Public Health, "Medical Marijuana Program Annual Report to the Rhode Island General Assembly," health.ri.gov, Sep. 2017
Vermont: Vermont Department of Public Safety, "Vermont Marijuana Registry Enrollment Charts," medicalmarijuana.vermont.gov, Dec. 2017
Washington: Washington State Department of Health, "Medical Marijuana Data and Statistics," doh.wa.gov, Apr. 25, 2018 (total cards created)
West Virginia: West Virginia Medical Cannabis Program, "Frequently Asked Questions: General Information," dhhr.wv.gov, Apr. 20, 2018
State and US Populations: US Census Bureau, "Annual Estimates of the Resident Population for the United States, Regions, States, and Puerto Rico: April 1, 2010 to July 1, 2017 (NST-EST2017-01)," census.gov (accessed May 16, 2018)