Sensitivity to a stress concentration is important for the development of pharmaceutical tablets as it is related to defects like capping. The Brittle Fracture Index (BFI) was introduced by Hiestand et al. to test this sensitivity. Recently, a more general index, based on the average stress criterion, was proposed as a generalized Hiestand approach. In this work, this new approach is tested on tablets obtained for several products and pressure levels, and results show the wide applicability of the new criterion. Furthermore, X-ray micro-computed tomography was used to link the tablet microstructure and the sensitivity to a stress concentration. A strong correlation was found between the size of the largest pores in the structure and the value of a(0) which quantify the sensitivity to a stress concentration in the generalized Hiestand approach. These results constitute the first attempt to link the brittle fracture propensity of tablets with their effective microstructure.