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1-(4-Bromophenyl)piperazine (street names: 4-bromo-piperein, 4-BP, brein) is structurally related to 1-(4-fluorophenyl)piperazine and to 1-(4-chlorophenyl)piperazine. The only difference is the halogen substituent type attached to the phenyl ring's para-position. In the case of NPSs from the methcathinone group, which are also neurotransmitter releasers, structure–activity studies demonstrated that the replacement of a fluorine or chlorine atom with a bromine atom resulted in a compound with more potency for the release of both dopamine and serotonin. The lowest dopamine selectivity, an additional consequence of these halogen replacements, results in lower abuse potential in favor of empathogenic properties[1].

[1] Magdalena Pop?awska. “Identification and structural characterization of three psychoactive substances, phenylpiperazines (pBPP and 3,4-CFPP) and a cocaine analogue (troparil), in collected samples.” Forensic Toxicology 40 1 (2022): 132–143.