The motivation of this study is to demonstrate the practicality of producing slow release and fast release products in a single-step hot melt extrusion (HME) process. HPMCAS as the carrier material showed good potential in monolithic controlled release formulations for the model drug, carbamazepine (CBZ). As binary formulations, CBZ-HPMCAS extrudates showed zero-order release over 24 h which was accompanied by the swelling of the extrudates. A range of functional excipients was used at low quantities to modulate the release rate. The release rates of the HME extrudates could be either accelerated by the incorporations of low quantities (5% w/w) of soluble additives or further sustained by adding lipid excipient, Gelucire 50/13. Clear phase separations of the soluble additives including crosscarmellose sodium, sodium starch glycolate, maltodextrin and lactose in the extrudates led to higher interior porosity and quicker erosion in comparison to the binary extrudates. The phase separated Gelucire in the extrudates led to the substantial swelling of the extrudates and resulted in further prolonged drug release. This study provided clear formulation strategies for modulating the drug release rate from controlled release formulation prepared directly by single-step HME. In addition, this research work also evaluates for the first time HME extrudates simultaneous swelling and drug release using this UV imaging technique. The whole dose cell of this instrumentation is utilised to provide insights into the dissolution process of solid dispersions prepared by HME.