A highly selective melanocortin-4 receptor antagonist cyclic peptide of the formula ##STR00001## where R.sub.1, R.sub.2, R.sub.3, R.sub.4a, R.sub.4b, R.sub.5, R.sub.6, R.sub.7, x, y and z are as defined in the specification, and a method of treating body weight disorders, including cachexia, sarcopenia and wasting syndrome or disease, and treating inflammation and immune disorders.