For a ketogenic diet to be effective, strict control of carbohydrate intake is paramount. Factors such as medications may upset this delicate balance. The aim of this commentary is to provide physicians who aretreating patients witha ketogenic diet, with a step-by-step guide. A list of unsuitable excipients was established. A flowchart with the title "Can this drug be prescribed to a patient following a ketogenic diet?" was then drafted. The first step is to determine the international nonproprietary name, dosage, form and composition. The amount of unsuitable excipients is calculated. Suitable alternatives may be discussed with the pharmacist. As a last resort, the ketogenic diet itself may need to be adapted. The answers provided are included in a database. Determining the amount of unsuitable excipients is a complex task requiring pharmaceutical expertise. Our flowchart can be used in order to provide a clear pathway for answering such questions.