This paper presents and analyses data obtained from the uniaxial compaction of pure pharmaceutical powders in terms of a number of mechanical properties, and correlates these data to some aspects of fracture mechanics. This includes seven different types of pharmaceutical drugs and excipients: alpha lactose, microcrystalline cellulose (Avicel PH 102), acetylsalicylic acid (Aspirin), dicalcium phosphate, magnesium carbonate, acetaminophen (Paracetamol) and starch. The powders were compacted to various ultimate normal stresses ranging between 25 and 246 MPa in an instrumented (force/displacement) single-ended axial compression in cylindrical die with planar punches. The results clearly demonstrate that, to some extent, the toughness of a tablet may be interpreted directly from some mechanical characteristics of its compliance response, i.e., the plastic work and the plasticity index, during the compaction process. (c) 2005 Elsevier Ltd. All rights reserved.