Benzylfentanyl

3 0 0 | | Flash point | 257.5 °C (495.5 °F; 530.6 K) | | Lethal dose or concentration (LD, LC): | | | LD50 (median dose) | 500 mg/kg (oral, as HCl salt, est.) | | Safety data sheet (SDS) | CATO Research Chemicals | | Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).

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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 Ki of 213 nM at the mu opioid receptor, binding around .mw-parser-output .sfrac{white-space:nowrap}.mw-parser-output .sfrac.tion,.mw-parser-output .sfrac .tion{display:inline-block;vertical-align:-0.5em;font-size:85%;text-align:center;margin-left:.1em;margin-right:.1em}.mw-parser-output .sfrac .num{display:block;border-bottom:1px solid}.mw-parser-output .sfrac .den{display:block;line-height:1.5em}.mw-parser-output .sr-only{border:0;clip:rect(0,0,0,0);clip-path:polygon(0px 0px,0px 0px,0px 0px);height:1px;margin:-1px;overflow:hidden;padding:0;position:absolute;width:1px}⁠1/200⁠ as strong as fentanyl itself, though it is still slightly more potent than codeine.

• Homofentanyl
• Isofentanyl