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2. United Nations Office on Drugs and Crime (UNODC) World Drug Report 2017 part 4, Market analysis of synthetic drugs, Amphetamine-type stimulants, new psychoactive substances
3. United Nations Office on Drugs and Crime (UNODC) Global SMART Update 17 - Fentanyl and its analogues 50 years on
4. European Monitoring Centre for Drugs and Drug Addiction (EMCDDA) European Drug Report 2017
5. Fentanyl, fentanyl analogs and novel synthetic opioids: A comprehensive review;Armenian;Neuropharmacology.,2017