The peptide has a sequence of 3 to 30 adjacent amino acids from the amino end of protein SNAP-25 and is useful as neuronal exocytosis inhibitor. The cosmetic and pharmaceutical compositions contain said peptide and optionally one or more peptides from the carboxyl end of SNAP-25. Said compositions are suitable for the treatment of facial wrinkles and asymmetry and pathological neuronal exocytosis-mediated pathological disorders and alterations.