Benzylfentanyl

 ( Piperidines ) 

Benzylfentanyl ( R-4129) is a fentanyl analog. It was temporarily placed in the US Schedule I by emergency scheduling in 1985 due to concerns about its potential for abuse as a designer drug, but this placement was allowed to expire and benzylfentanyl was formally removed from controlled substance listing in 2010, after the DEA's testing determined it to be "essentially inactive" as an opioid. It was added as a List I precursor instead in 2020 after it was determined that it was being used in fentanyl manufacture, which was previously thought to be beyond the technical capability of illicit labs. Benzylfentanyl has a K of at the mu opioid receptor, binding around as strong as fentanyl itself, though it is still slightly more potent than codeine.

• Homofentanyl
• Isofentanyl