What this guy said /u/Staffatwork:
Yes it is a known fact.
The dramatic escalation of incarceration for drug offenses has been accompanied by profound racial/ethnic disparities. Overall, two-thirds of persons incarcerated for a drug offense in state prison are African American or Latino. These figures are far out of proportion to the degree that these groups use or sell drugs. A wealth of research demonstrates that much of this disparity is fueled by disparate law enforcement practices. In effect, police agencies have frequently targeted drug law violations in low-income communities of color for enforcement operations, while substance abuse in communities with substantial resources is more likely to be addressed as a family or public health problem.
http://www.sentencingproject.org/doc/dp_raceanddrugs.pdf
Black Americans were nearly four times as likely as whites to be arrested on charges of marijuana possession in 2010, even though the two groups used the drug at similar rates, according to new federal data.
http://www.nytimes.com/2013/06/04/us/marijuana-arrests-four-times-as-likely-for-blacks.html?_r=0
On average, blacks receive almost 10% longer sentences than comparable whites arrested for the same crimes. At least half this gap can be explained by initial charging choices, particularly the filing of charges carrying mandatory minimum sentences. Prosecutors are, ceteris paribus, almost twice as likely to file such charges against blacks.
http://www.fjc.gov/public/pdf.nsf/lookup/NSPI201213.pdf/$file/NSPI201213.pdf