Number of Legal Medical Marijuana Patients
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?
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.