A peptide with the following sequence YCQKFLWTCDSERPCCEGLVCRLWCKIN (SEQ ID NO 1) or a derivative thereof, and nucleic acids coding for the peptide having the sequence (SEQ ID NO 1). Also the use of this peptide as an antagonist and/or reverse agonist of T-type calcium channels. A use of the peptide for preparing a drug, in particular an analgesic one.