Formulations are formed of a diblock copolymer (X--Y) having a hydrophilic block X comprising residues of monomer x, and a hydrophobic block Y comprising residues of monomer y; an additive selected from an amino acid and an oligopeptide. Upon admixture with water, the formulations form drug delivery vehicles, preferably in micellar form. The inclusion of amino acid and/or oligopeptide provides for the formation of micelles at an enhanced rate, and/or provides the formation of micelles having an enhanced ability to incorporate drug(s), and/or provides the formation of micelles having advantageous physical characteristics.