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Orphine analogues (inactive)

Orphine analogues, also known as brorphine analogues or "orphines" or benzimidazol-2-ones,  are a class of potent synthetic opioids that have substituted piperidine benzimidazolone structures and are related to the internationally controlled substances bezitramide (1969) and brorphine (2022).

Orphine analogues are structurally related compounds derived from a common core scaffold, usually a benzimidazolone (Figure 1).

 
Figure 1: Orphine analogues.
Note: The simplest structure is orphine, which consists of a benzimidazolone core connected to a phenylethylpiperidine group. Chlorphine is very similar to the orphine structure, differing only by the presence of a chlorine atom on its phenyl ring. Brorphine is structurally related to chlorphine with the distinction being the replacement of chlorine with a bromine. Another substance, 5,6-Dichloro desmethylchlorphine lacks a methyl group on the side chain, resulting in a phenylmethyl piperidine. It also has two chlorines linked to the benzimidazole ring. N-propionitrile chlorphine (cychlorphine) extends the chlorphine structure by adding a propionitrile group to the benzimidazole nitrogen. Spirochlorphine presents the most different structure. It replaces the benzimidazole ring with a spirocyclic system while retaining the 4-chlorophenylethyl group. Etodezitramide is more closely related to bezitramide.


Brorphine generally acts as a full mu-opioid receptor agonist, with greater potency than morphine, and comparable or slightly lower potency than fentanyl. The substance has been identified in various drug sample forms: as powder, crystal, tablet or capsule form, including as falsified opioid medicines.[1] Moreover, brorphine has been associated with serious adverse effects, including deaths.[2] With no known therapeutic use, brorphine poses a significant risk to public health and safety.[1]

Vandeputte et al. have explored the pharmaco-toxicological, opioid-like effect profile of four brorphine analogues (orphine, fluorphine, chlorphine and iodorphine). In vitro characterization indicated that chlorphine, brorphine and iodorphine were generally the most active mu-opioid receptor agonists. In mouse experiments, chlorphine and brorphine induced the highest levels of antinociception; different analogues produced pronounced respiratory depressant effects, with observed differences in sensitivity to naloxone. Based on these findings, the authors concluded that brorphine analogues are opioid agonists with the potential to cause substantial harm, including respiratory depression.[3] More research is needed to further elucidate the effect profile and overdose management of brorphine analogues in humans.

For further information, please refer to the UNODC Early Warning Advisory News issued May 2025 and trend information in drug samples and toxicology samples.

References

[1] World Health Organization, 44th WHO ECDD Summary assessments, findings and recommendations, 11-15 October 2021, Available at: 44 ECDD_UNSG_Annex1_15112021$2021-11-16-18-45-27~.docx (accessed on 13 May 2025).

[2] For further information, please see: United Kingdom, Advisory Council on the Misuse of Drugs, “ACMD advice on 2-benzyl benzimidazole and piperidine benzimidazolone opioids”, 29 January 2025 and CFSRE Emerging Global Synthetic Opioid Threats: Benzimidazol-2-ones – The Orphines, 30 January 2026.

[3] For more information, please see: Vandeputte and others, “Elucidating the harm potential of brorphine analogues as new synthetic opioids: Synthesis, in vitro, and in vivo characterization”, Neuropharmacology, vol. 260 (December 2024).

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