A cyclic peptide of the structural formula: or a pharmaceutically acceptable salt thereof, wherein R1, R2, R3, R5, R6, m, n and p are as defined. Further provided are compositions for treatment of sexual dysfunction in mammals, including male sexual dysfunction, such as erectile dysfunction, and female sexual dysfunction, by administration of a cyclic peptide including a C-terminus —OH group. Routes of administration include injection, oral, urethral, vaginal, nasal and mucosal administration.