The inter-tablet coating uniformity is a critical quality attribute in active coating processes. In this project an active coating process is performed in order to produce a fixed dose combination of a sustained release formulation in the tablet core and an immediate release dose in the coating layer. The tablet cores consist of a push-pull osmotic system containing nifedipine as API (Adalat GITS). They are coated with Candesartan cilexetil as a second API. As the inter-tablet coating uniformity is a critical quality attribute to comply with regulatory requirements, the purpose of this work is to enhance the process understanding and to optimize the coating process with regard to the coating uniformity. Besides experimental investigations, PAT tools such as Raman spectroscopy  and terahertz pulsed imaging  have been applied to study this active coating process. In recent years, numerical simulations of coating processes have been gaining interest as analytical tool . The discrete element method (DEM) in particular is suitable to simulate the tablet motion . In this project, both experimental and numerical analysis of an active coating process is combined to investigate the influence of different process parameters with respect to the optimization of the coating uniformity.