This is a phase 2b, multicenter, prospective, randomized, double-blind, placebo-controlled, crossover study in symptomatic celiac disease patients attempting a GFD for at least one year prior to screening. Seropositive patients (blood test confirmed at Visit 0) will be scheduled for a Screening Visit (Visit 1) whereas seronegative patients will be discontinued from study participation (screen failures). Patients who meet Visit 1 protocol enrollment criteria will be enrolled and begin the first of two 6 week periods.