[D-Arg1,D-Phe5,D-Trp7,9,Leu11]-Substance P acetate is a broad-spectrum neuropeptide inverse agonist and antagonist. It acts as a full inverse agonist for the ghrelin receptor (EC50 = 5.2 nM) and antagonist at tachykinin, bradykinin, CCK, and bombesin receptors. It induces apoptosis and inhibits cancer cell growth in vitro.