An isolated, synthetic or recombinant χ-conotoxin peptide having the ability to inhibit neuronal amine transporter comprising the following sequence of amino acids:Cys Cys Gly Tyr Lys Leu Cys Xaa5 Xaa6 Cys SEQ ID NO. 3where Xaa5 and Xaa6 are independently absent or represent any amino acid residue except Cys；or a sequence in which Gly, Tyr, Lys or Leu are subject to conservative amino acid substitution or side chain modification；with the proviso that the peptide is not χ-MrIA, χ-MrIB, Mar2, CMrVIA, Bn1.5, Mr1.3 or Au1.4；or a salt, ester, amide, prodrug or cyclised derivative thereof.In particular embodiments the peptide isXaa2 Xaa3 Xaa4 Cys Cys Gly Tyr Lys Leu Cys Xaa5 Xaa6 Cyswhere Xaa2 is Arg, BHK, Om, DArg or DMK； Xaa3 is selected from Gly, Asp, Lys, Arg, Ala, Nle and Ser,Xaa4 is selected from Leu, Nle, Val, Ile, Thr, Ala and Abu.
