From the Executive Summary: "The 2015 National Drug Threat Assessment (NDTA) is a comprehensive assessment of the threat posed to the United States by the trafficking and use of illicit drugs. The drug section of this report is arranged in ranking order based on the level of threat each drug presents. The threat level for each drug is determined by strategic analysis of the domestic drug situation during 2014, based on law enforcement, intelligence, and public health data available for the period. […] A full discussion for each of these drugs cannot be undertaken without first examining the criminal groups that supply these substances to distributors and users in the United States."
Drug Enforcement Administration: http://www.dea.gov/