This study will evaluate the efficacy and safety of ragweed sublingual tablet (SCH 39641/MK-3641) compared with placebo in participants with ragweed-induced rhinoconjunctivitis over a one-year period. It is expected that ragweed allergic participants on one of the active arms of the trial will have decreased allergic rhinoconjunctivitis symptoms and require less allergy rescue medications during ragweed pollen season.