Common side effects of using iron ferrous sulfate include constipation, green or dark stools, nausea, loss of appetite and diarrhea, according to Drugs.com. Patients may experience stomach cramps, stomach pain and vomiting.
Severe side effects of iron ferrous sulfate include blood in stool, black tarry stool, vomit that resembles coffee grounds, and severe allergic reactions such as hives and tightness in the chest, reports Drugs.com.
Gastrointestinal side effects of taking iron ferrous sulfate are anorexia, heartburn, constipation and diarrhea, notes Drugs.com. These side effects are often dose-related, and they may reduce when doctors prescribe smaller doses and increase the dose gradually. Liquid preparation of iron ferrous sulfate may stain the teeth. To prevent this side effect, patients can dilute the liquid iron ferrous sulfate in water or juice and take it using a straw. Local side effects include gangrene, while metabolic side effects include decreased thyroxine absorption. A rare side effect is secondary hemochromatosis, or iron overload.
Iron ferrous sulfate may cause allergic reactions in people who are allergic to sulfate or other medications' tartrazines, according to MedlinePlus. Patients should ask for a list of ingredients to ensure they are not allergic to any of them. Ferrous sulfate may interact with certain drugs, including antacids and antibiotics, notes Drugs.com.