The purpose of this study was to evaluate sustained drug release after melt granulation and heat treatment. Theophylline (anhydrous) and phenylpropanolamine hydrochloride (PPA) were used as model drugs. Compritol 888 ATO (Glyceryl Behenate NF) was incorporated as the wax matrix material. Formulations with drug:wax in 3:1 and 1:1 ratios were evaluated. Tablets were made by dry blending or melt granulation; some of the tablets were heat treated at 80 degrees C for 30 min. Tablets with or without heat treatment were tested for drug release using in vitro drug dissolution. The results showed that melt granulation gave slower drug release than dry blending. Heat treatment further retarded drug release for both dry blending and melt granulation. The drug release rates for theophylline were slower than for PPA at the same wax level and processing method. The drug release profiles were linear using a square root of time scale. In conclusion, melt granulation and heat treatment slowed drug release for the wax matrix-controlled release tablets. Heat treatment of the tablets made by melt granulation further retarded drug release. Heat treatment redistributed the wax, forming a new matrix system with higher tortuosity. The application of melt granulation or heat treatment can successfully retard drug release.