World Health Organization 2018:
Cyclopropylfentanyl was synthesized by Paul Janssen as described in the patent literature in 1965 (U.S.) and 1968(France). It has a chemical structure that is similar to fentanyl. Based primarily on reports of overdoses attributed to cyclopropylfentanyl describing naloxone-reversible loss of consciousness, depressed respiration, and miosis, it appears to be a potent mu opioid receptor agonist. As such, its pharmacology and toxic effects are likely to be similar to fentanyl. It currently has no legitimate medical or veterinary uses and is relatively easy to manufacture. Cyclopropylfentanyl is being sold as heroin, an adulterant in heroin, or as counterfeit oxycodone pills. Cyclopropylfentanyl has been detected in white or off-white powders and, to a lesser extent, in liquids and in tablets.

Excerpt from World Health Organization (PDF 14 pages):
https://www.who.int/medicines/access/controlled-substances/Cyclopropylfentanyl.pdf?ua=1

EMCDDA - Europol Joint Report 2018:
Data suggests that cyclopropylfentanyl may be an opioid narcotic analgesic in humans, and, as such, may have an abuse liability and dependence potential; overall, these effects may be broadly comparable to fentanyl.

The most serious acute health risk posed by cyclopropylfentanyl is likely to be respiratory depression, which in overdose is life-threatening. The antidote naloxone should reverse this respiratory depression.

Cyclopropylfentanyl has been available in the European Union since at least June 2017. It has been detected in 5 Member States and Norway where it has been seized as a powder, liquids, and tablets. While the detected quantities are relatively small, they include 3 seizures of bulk quantities of powder weighing approximately between 500 and 600 g each. Overall, the quantities detected should be seen within the context of the high potency that is typical of the fentanils. There are indications that the cyclopropylfentanyl currently available on the market is synthesised by chemical companies based in China. Cyclopropylfentanyl is sold online often under the guise of a 'research chemical'. It is available, and, has been seized, in wholesale amounts and in consumer amounts. A total of 60 deaths with confirmed exposure to cyclopropylfentanyl have been reported to the EMCDDA by Sweden (59 cases) and Norway (1). In at least 23 of the deaths, cyclopropylfentanyl was the cause of death or contributed to the death.

Cyclopropylfentanyl is sold and used as a substitute for illicit opioids and prescription opioids. Similar to other fentanils, serious concerns exist that the substance could be supplied surreptitiously to a range of drug users.

Cyclopropylfentanyl does not appear to have any recognised human or veterinary medical use in the European Union.

Cyclopropylfentanyl Joint Reports (PDF 16 pages):
https://www.emcdda.europa.eu/system/files/publications/7926/20181014_TDAS18001ENN_PDF.pdf

Cyclopropylfentanyl:

• An opioid analgesic
• An analog of fentanyl
• Has been sold as a designer drug

Side effects of fentanyl analogs are similar to those of fentanyl itself which include itching, nausea and potentially serious respiratory depression, which can be life-threatening

Between June and December 2017, a total of 78 cyclopropylfentanyl-related deaths with analytical confirmation in post-mortem samples were reported by various European countries. Another 115 deaths involving cyclopropylfentanyl were reported from the United States in 2017