Patients sometimes appear for dental appointments after consuming alcohol or marijuana. There is presently no consensus standard of care in this area, and dentists vary in their responses to such patients. This paper includes interviews with practitioners and a review of the relevant biochemical and physiological science. The ethics of various ways to handle this challenging situation are examined, and evidence-based recommendations for dental practice are offered. While there is reason for caution, the authors conclude that a blanket "do not treat" policy is unwarranted. Informed consent and transportation safety issues pose significant moral challenges when a dental patient is "high."