As you're probably aware, black Americans are arrested for marijuana possession far more frequently than whites. You may also know that there's not much evidence that black people consume marijuana with greater regularity than whites do.
And more blacks say they've never used marijuana:
Similarly, the vast majority of counties arrest blacks at a higher rate than whites, with some having a disparity of greater than 10 to 1:
And this includes a lot of urban areas that are highly populated and liberal-leaning. Cook County, Illinois, which includes Chicago, has one of the largest disparities of any county. So does New York County (Manhattan) and Kings County, N.Y. (Brooklyn):
How important is this? Well, while making up a quite small share of our prison population, marijuana possession charges make up nearly half of total drug arrests:
The report does suggest that legal reforms, in particular decriminalization, is effective at reducing overall arrest rates. Massachusetts decriminalized the possession of small amounts of marijuana in 2009, and arrests dropped an enormous amount:
But it's hard to make the case that decriminalization made enforcement more equitable. Indeed, as Stanford med school Professor Keith Humphreys notes, the states that have legalized or decriminalized marijuana to date all have smaller-than-average black populations. That suggests that whatever benefits casual marijuana users have received from those policies have mainly accrued to white smokers.