Which of the following is a common adverse effect of iron supplements?

Iron supplements are often used to treat or prevent iron deficiency anemia and can have several side effects. Nausea is a common adverse effect associated with iron supplementation due to its irritative properties on the gastrointestinal tract. The body's reaction to the introduction of iron can lead to stomach upset, which may result in feelings of nausea.

The other options, such as rash, dry cough, and headaches, are less commonly related to iron supplements. While they can occur, they are not typical side effects that most patients report. Understanding nausea as the most frequently encountered adverse effect helps in educating patients on what to expect and how to manage it, such as taking the supplement with food or adjusting the dosage if necessary.