OsteoSheath 4 is the same product as OsteoSheath except that OsteoSheath 4 is a smaller, easier to swallow tablet, so instead of taking three tablets with OsteoSheath, you take four smaller tablets;; hence the "4" in OsteoSheath 4. Gluten free. Now with double the vitamin D and zinc added. Microcrystalline Hydroxyapatite (MCHC), Calcium Amino Acid Chelate, Calcium Citrate, Enhanced Osteo Support, Calcium Building Complex.