Allergic rhinitis (AR) can, by itself, introduce significant sedation and impairment of cognition and performance. AR can also impede restorative sleep, resulting in increased fatigue and decreased daytime performance. It is not clear whether improved alertness resulting from blocking histamine production offsets the sedating effects of antihistamines or whether the effects of disease and treatment combine to create even greater sedation. This article reviews and integrates this literature, offers conclusions based on the collective evidence, and suggests guidelines for future research.