The astringent action of iron preparations sometimes produces gastrointestinal irritation and abdominal pain with nausea and vomiting when administered orally. These irritant side-effects are usually related to the amount of elemental iron taken rather than the type of preparation. Other gastrointestinal effects may include either diarrhea or constipation. Side effects may be reduced by administration with or after food (rather than an empty stomach) or by beginning therapy with a small dose and increasing gradually. Folic acid is generally tolerated. Gastrointestinal disturbances and hypersensitivity reactions have been reported rarely.