This randomized, crossover study is to evaluate the early effectiveness, defined as effect on intragastric pH during the first 4 hours after dosing, of Zegerid, Prilosec over-the-counter (OTC) Tablets, and placebo on the 4th day of treatment to inhibit acid secretion. Additional purposes are to:

1. provide pharmacodynamic evidence comparing 24-hr inhibition of acid secretion on the 1st, 4th, and 11th days of dosing with each of the indicated treatments;
2. compare Zegerid and Prilosec OTC for achieving their steady-state effects for controlling 24-hr gastric acidity at steady-state on the 4th and 11th day of dosing.
3. evaluate early effectiveness, defined as effect on intragastric pH during the first 4 hours after administration, of Zegerid, Prilosec OTC Tablets, and placebo on acid inhibition at steady-state when administered on the 11th day of dosing.

Participants were randomized in a 3-way crossover design and received, in random order, Zegerid OTC Capsules (20 mg omeprazole and 1100 mg sodium bicarbonate), Prilosec OTC Tablets (20 mg-equivalent omeprazole), and Placebo Capsules. Participants received each treatment for 11 days. There was a minimum of a 2-week washout period between treatment arms.

Inclusion Criteria:

• Male or non-lactating, non-pregnant female subjects who are 18-65 years of age.
• Physical examination findings within normal limits for age.

Exclusion Criteria:

• History of hypersensitivity, allergy or intolerance to omeprazole, or other proton pump inhibitors
• History of peptic ulcer disease or other acid related gastrointestinal symptoms or heartburn with a frequency of more than one/month.
• Participation in any study of an investigational treatment in the 30 Days before Screening or participation in another study at any time during the period of this study
• Any significant medical illness that would contraindicate participation in the study
• Gastrointestinal disorder or surgery leading to impaired drug absorption
• Any abnormal Screening laboratory value that is clinically significant in the investigator's opinion
• Current use of any prescription or OTC medications that affect gastrointestinal function.
• Currently using or having a history of frequent use of antacids, OTC or prescription (Rx) histamine-2 (H2) receptor antagonists, or OTC or Rx use of proton pump inhibitors.