Maximum Strength Zantac 150 Acid Reducer, a nonprescription strength of Zantac is now available for prevention and relief of heartburn associated with acid indigestion and sour stomach. The ingredient in MAXIMUM STRENGTH Zantac 150, ranitidine, has been prescribed by doctors for years to treat millions of patients safely and effectively. The active ingredient in MAXIMUM STRENGTH Zantac 150 has been taken safely with many frequently prescribed medications.