Orally administered iron, due to its astringent action, produces gastrointestinal irritation and abdominal pain with nausea and vomiting. These irritant side effects are usually related to the amount of elemental iron taken rather than the type of preparation. Other effects may include either diarrhea or constipation. Side effects may be reduced by administration with or after food or by starting therapy with a small dose and increasing gradually.
May cause temporary staining of teeth. Stools may appear darker in color.
Prolonged folic acid therapy may cause a decrease in vitamin B12 serum concentration.