African Americans are arrested for violating marijuana possession laws at nearly four times the rates of whites, yet both ethnicities consume marijuana at roughly the same rates.
Specifically, the The American Civil Liberties Union report The War on Marijuana In Black and White (2013) concluded: "[O]n average, a Black person is 3.73 times more likely to be arrested for marijuana possession than a white person, even though Blacks and whites use marijuana at similar rates. Such racial disparities in marijuana possession arrests exist in all regions of the country, in counties large and small, urban and rural, wealthy and poor, and with large and small Black populations. Indeed, in over 96% of counties with more than 30,000 people in which at least 2% of the residents are Black, Blacks are arrested at higher rates than whites for marijuana possession."
A 2017 analysis of New Jersey arrest data found that African Americans are three times more likely than whites to be arrested for violating marijuana possession laws (The American Civil Liberties Union, Unequal & Unfair: NJ's War on Marijuana Users, 2017)
An analysis of Maryland arrest data determined that African Americans accounted for 58 percent of all marijuana possession arrested despite comprising only 30 percent of the state's population. (The American Civil Liberties Union, The Maryland War on Marijuana in Black and White, 2013)
Prior to the enactment of decriminalization, an analysis of marijuana possession arrest data in Chicago by reported that the ratio of black to white arrests for cannabis possession violations is 15 to 1. (Chicago Reader, The Grass Gap)