In at least one year, the white usage rate was higher. The others, the black usage rate was higher, but in no year were results for the two races that different. For young people ages 18-25, the rates of use are higher for whites:
Of course, this doesn't translate to roughly equal arrest rates. Not even close:
And this is a uniform phenomenon. It's not that some states treat the races equally and others treat them really unequally. Only in Hawaii are the rates even close to equal, and that's biased by the fact that blacks make up only 1.6 percent of the population. In the state with the second-lowest disparity, Alaska, blacks are 1.6 times more likely to be arrested. In the state with the biggest, Iowa, blacks are 8.34 times more likely to be arrested. D.C. has the second biggest; in the District, blacks are 8.05 times more likely to be arrested.
Obviously, being arrested without going to jail is a lot better than getting arrested and going to jail. But it's still a major nuisance, leading to fines, long hours of community service and thousands of dollars in legal fees.
But interestingly, the racial disparity in arrests did not fall at all:
In 2008, the black arrest rate in Massachusetts was 3.41 times the white arrest rate. In 2009, it was 5.4 times the white arrest rate. Now, the importance of the disparity diminishes when overall arrests are falling that dramatically, and there's no reason to think that decriminalization caused the disparity to increase; in 2010, it fell back down to 3.81.