N-phenyl-N-[1-(2-phenylethyl)-4-piperidyl]cyclopentanecarboxamide (Cyclopentylfentanyl): Cyclopentylfentanyl was identified in 10 mL of colourless liquid seized by Swedish Police in Jönköping on 29 August 2016. The substance was analytically confirmed using GC-MS, NMR and LC-HRMS by the Swedish National Forensic Centre (NFC). Cyclopentanylfentanyl belongs to the 4-anilidopiperidine class of synthetic opioids. It is structurally similar to the opioids tetrahydrofuranylfentanyl and to furanylfentanyl, which is currently the focus of an EMCDDA-Europol Joint Report. Cyclopentylfentanyl differs from tetrahydrofuranylfentanyl due to the presence of cyclopentane in place of the fully saturated furanyl ring and differs from furanylfentanyl due to the presence of cyclopentane in place of the furan ring. Thus the molecular weight of cyclopentylfentanyl differs from both tetrahydrofuranylfentanyl and furanylfentanyl by only 2 atomic units. There are no published data on the pharmacology or toxicology of cyclopentylfentanyl. Based on its chemical structure and on the similarity to furanylfentanyl, the substance may display opioid-like effects. These include: euphoria, nausea, vomiting, sedation and respiratory depression.