The present invention relates to pharmaceutical formulations for the release of an active principle (AP) over a sustained period of time. The invention relates to a liquid formulation comprising at least one active principle (AP) and an aqueous suspension based on colloidal particles of a polymer (PO), wherein said formulation satisfies the following four conditions: (a) the PO is a polyamino acid comprising glutamic residues, wherein some glutamic residues each carry a pendant cationic group (CG), said CG being identical or different from one another, and other glutamic residues each carry a pendent hydrophobic group (GH), said GH being identical or different from one another, (b) the pHf value of the pH of said formulation is between 3.0 and 6.5; (c) at the pHf value, the PO forms a colloidal solution which associates spontaneously and noncovalently with the AP; (d) 1 ml of said formulation precipitates during mixing with a volume of 1 ml of a test buffer solution Tp.