1. UNODOC World Drugs Report http://www.unodc.org/wdr2016/ 2017
2. EMCDDA European Drug Report 2016: Trends and Developments http://www.emcdda.europa.eu/publications/edr/trends-developments/2016_en 2017
3. An expanding world of novel psychoactive substances: Opioids;Zawilska;Front Psych,2017
4. Notes from the field: Increase in fentanyl-related overdose deaths - Rhode Island, November 2013-march 2014;Mercado-Crespo;MMWR,2014
5. US Department of Justice Drug Enforcement Administration National Drug Treat 2016 https://www.dea.gov/resource-center/2016%20NDTA%20Summary.pdf 2017