NPFF1-R antagonist 1 (compound 8b), a piperidine analogue, is a potent neuropeptide FF (NPFF) receptor antagonist. NPFF1-R antagonist 1 is 15-fold selective for the NPFF1-R subtype, with K i values of 211 nM and 3270 nM for NPFF1-R and NPFF2-R, respectively.