Disclosed herein are novel pharmaceutical agents and compositions, as well as novel methods, to enhance the absorption of polypeptide drug substances that normally display little if any absorbability if administered orally. Also disclosed are novel compositions and methods to significantly enhance the bioavailability and pharmacological efficacy of polypeptide drug substances whether administered orally or parenterally. The pharmaceutical agents of the invention comprise a carrier moiety selected from cinnamoyl, 3,4-methylenedioxycinnamoyl and 3,4,5-trimethoxycinnamoyl. The carrier moiety is chemically linked to a therapeutically active pseudo-peptide of 2-40 residues with one or more reduced peptidic bonds.
