Metformin hydrochloride shows high solubility and incomplete absorption in biological system. To control the release pattern of such a drug, interpolymer complexes (IPCs) have a greater advantage over the individual polymers. In view of that, hydrophilic chitosan and hydroxypropyl methylcellulose (HPMC K4M) IPCs are developed at different ratios (1 : 1, 1 : 2, 1 : 3, and 1 : 4) and characterized by thermogravimetric analysis, Fourier transform infrared spectroscopy, and X-ray diffraction studies. Different formulations (F1–F10) are developed using individual polymers and IPCs of hydrophilic polymers. Addition of hydrophobic shellac and beeswax to IPCs extends the release rate of metformin. The physical properties and drug content values of the tablets were determined and found to be within the standard limits. Based on the results of dissolution study, it is found that formulation F10 containing 1 : 4 IPC and beeswax has shown good sustained release for a period of more than 10 h. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 41018.