What are the side effects of taking iron supplements?

Mostly GI Distress. Side effects from taking iron supplements are most often diarrhea or constipation and epigastric abdominal discomfort. Taken after a meal, side effects decrease, but there is an increased risk of interaction with other substances. Black stools are not uncommon, but harmless. Liquid form can discolor the teeth and intramuscular injections can be painful and leave a brown discoloration.