Seasonal allergic rhinitis (SAR), also known as hay fever, is an allergic reaction in the upper airways that occurs when sensitized individuals encounter airborne allergens (typically tree, grass, and weed pollens and some molds). Although pollen seasons vary across the United States, generally, tree pollens emerge in the spring, grass pollens in the summer, and weed pollens in the fall. Outdoor molds generally are prevalent in the summer and fall. SAR is distinguished from perennial allergic rhinitis (PAR), which is triggered by continuous exposure to house dust mites, animal dander, and other allergens generally found in an individual's indoor environment. Patients may have either SAR or PAR or both (i.e., PAR with seasonal exacerbations). The four defining symptoms of allergic rhinitis are nasal congestion, nasal discharge (rhinorrhea), sneezing, and/or nasal itch. Many patients also experience eye symptoms, such as itching, tearing, and redness. Additional signs of rhinitis include the "allergic salute" (rubbing the hand against the nose in response to itching and rhinorrhea), "allergic shiner" (bruised appearance of the skin under one or both eyes), and "allergic crease" (a wrinkle across the bridge of the nose caused by repeated allergic salute). SAR can adversely affect quality of life, sleep, cognition, emotional life, and work or school performance. Treatment improves symptoms and quality of life. Treatments for SAR include allergen avoidance, pharmacotherapy, and immunotherapy. Although allergen avoidance may be the preferred treatment, for SAR, total allergen avoidance may be an unrealistic approach, as it may require limiting time spent outdoors. Thus, pharmacotherapy is preferable to allergen avoidance for SAR symptom relief. Although there are multiple guidelines for the treatment of allergic rhinitis, the guidelines are not consistently based on systematic reviews of the literature and often do not address the treatment of SAR in children and pregnant women. Guidelines generally support the use of intranasal corticosteroids as first-line treatment of moderate/severe SAR. However, agreement is lacking about four other issues of importance to patients and clinicians: First-line treatment for mild SAR The comparative effectiveness and safety of SAR treatments used in combination with each other for both mild and moderate/severe SAR The comparative effectiveness of as-needed use compared with daily dosing The comparative effectiveness and harms of SAR treatments for eye symptoms and asthma symptoms that often co-occur with SAR This review addresses the four issues above. The scope of this review is comparisons across pharmacologic classes. Key Questions addressed include: KQ1. What is the comparative effectiveness of pharmacologic treatments, alone or in combination with each other, for adults and adolescents (12 years of age or older) with mild or with moderate/severe SAR? KQ2. What are the comparative adverse effects of pharmacologic treatments for SAR for adults and adolescents (12 years of age or older)? KQ3. For the subpopulation of pregnant women, what are the comparative effectiveness and comparative adverse effects of pharmacologic treatments, alone or in combination with each other, for mild and for moderate/severe SAR? KQ4. For the subpopulation of children (less than 12 years of age), what are the comparative effectiveness and comparative adverse effects of pharmacologic treatments, alone or in combination with each other, for mild and for moderate/severe SAR?