Stomach acid is needed for the vitamin B12 in food to be absorbed. H-2 blocker drugs reduce stomach acid and may therefore inhibit absorption of the vitamin B12 naturally present in food. However, the vitamin B12 found in supplements does not depend on stomach acid for absorption.¹ Lab tests can determine vitamin B12 levels in people.

Stomach acid may increase absorption of iron from food. H-2 blocker drugs reduce stomach acid and are associated with decreased dietary iron absorption.² The iron found in supplements is available to the body without the need for stomach acid. People with ulcers may be iron deficient due to blood loss. If iron deficiency is present, iron supplementation may be beneficial. Iron levels in the blood can be checked with lab tests.

Some evidence indicates that other vitamins and minerals, such as folic acid ³ and copper ,⁴ require the presence of stomach acid for optimal absorption. Long-term use of H-2 blockers may therefore promote a deficiency of these nutrients. Individuals requiring long-term use of H-2 blockers may therefore benefit from a multiple vitamin/mineral supplement .

Some evidence indicates that other vitamins and minerals, such as folic acid ⁵ and copper ,⁶ require the presence of stomach acid for optimal absorption. Long-term use of H-2 blockers may therefore promote a deficiency of these nutrients. Individuals requiring long-term use of H-2 blockers may therefore benefit from a multiple vitamin/mineral supplement .

In healthy people, a magnesium hydroxide / aluminum hydroxide antacid, taken with famotidine, decreased famotidine absorption by 20–25%.⁷ People can avoid this interaction by taking famotidine two hours before or after any aluminum/magnesium-containing antacids. Some magnesium supplements such as magnesium hydroxide are also antacids.