Adults with normal bowel function have a very low risk of iron overload from food. However, acute intakes of more than 20 mg/kg of iron from supplements or medications can lead to gastric upset, constipation, nausea, abdominal pain, vomiting, and fainting, especially if food is not taken at the same time. Taking supplements containing 25 mg of elemental iron or more may also reduce zinc absorption and plasma zinc concentrations. In severe cases (eg, single ingestion of 60 mg/kg), iron overdoses can lead to multiple organ failure, coma, convulsions, and even death.
Between 1983 and 2000, at least 43 children in the United States died from ingesting supplements containing high doses of iron (36-443 mg iron/kg body weight). Accidental ingestion of iron supplements caused about one-third of poisoning deaths among children reported in the United States between 1983 and 1991.
In 1997, the FDA began requiring oral supplements containing more than 30 mg of elemental iron per dose to be sold in a single dose package with strong warning labels. At the same time, many manufacturers have voluntarily replaced the sugar coating on iron tablets with film coatings.