The present invention relates to a cyclic peptide and to its use as an inhibitor of clostridium neurotoxins, preferably tetanus and botulinum neurotoxins. The peptide of the invention is useful in the treatment and/or prevention of the diseases caused by said clostridium neurotoxins. The invention also relates to the nucleic acid that codifies it, to a cell, a pharmaceutical composition and a kit that comprises it.