Ragweed is an important cause of allergic rhinitis with or without conjunctivitis (AR/C) in North America and elsewhere. Allergen immunotherapy enabling safe patient self-administration is considered an unmet clinical need. Allergy immunotherapy tablet (AIT) treatment has shown promising efficacy and safety for grass allergy but has not been assessed for ragweed allergy. To evaluate efficacy and safety of 2 short ragweed AIT doses in patients with AR/C. Adults with ragweed pollen-induced AR/C were randomized 1:1:1 to daily ragweed AIT (6 or 12 Amb a 1 units) or placebo before, throughout, and after ragweed season (approximately 52 weeks). Patients could use predefined allergy rescue medications in season. Efficacy end points included peak and entire season total combined score (TCS) and its components daily symptom score (DSS), and daily medication score (DMS). Safety assessments included adverse events. A total of 565 patients were randomized. During peak season, the 6- and 12-Amb a 1 unit ragweed AIT doses showed 21% (-1.76 score) and 27% (-2.24 score) improvement in TCS vs placebo (P < .05). The 6- and 12-Amb a 1 unit AIT doses significantly improved DSS and DMS vs placebo (P < .05). Peak and entire season efficacy were comparable. The 12-Amb a 1 unit AIT dose reduced peak-season TCS vs placebo by 21% and 25% in subgroups with and without local application-site reactions, respectively. Most treatment-related adverse events were mild, oral reactions; no systemic allergic reactions were reported. One patient in the 6-Amb a 1 unit group received epinephrine at an emergency facility for sensation of localized pharyngeal edema. In this trial, ragweed AIT was effective and well tolerated in ragweed-allergic North American adults. clinicaltrials.gov Identifier: NCT00783198. Copyright © 2013 American College of Allergy, Asthma & Immunology. Published by Elsevier Inc. All rights reserved.