ASTI is a guideline-based decision support system for therapeutic prescribing in primary care with two modes of interaction. The “critic mode” operates as a reminder system to detect non guideline-compliant physician drug orders, whereas the “guided mode” operates on demand and provides physician guidance to help her establishing best recommended drug prescriptions for the management of hypertension. A preliminary evaluation study was conducted with 10 GPs to test the complementary nature of both modes of decision support. Results tend to validate our assumption that reminder-based interaction is appropriate for simple cases and that physicians are willing to use on-demand systems as clinical situations become more complex.