What gastrointestinal disturbances are commonly associated with ferrous supplements?

Ferrous supplements, commonly used to treat iron deficiency anemia, can lead to gastrointestinal disturbances primarily due to their effect on the digestive system. The correct answer identifies these reactions as constipation or diarrhea, which are well-documented side effects associated with iron supplementation.

Iron can affect the gastrointestinal tract in various ways. It may increase the transit time through the intestines, leading to constipation in some individuals. Conversely, for others, it might cause an increase in fluid secretion or alter gut motility, resulting in diarrhea. This variability in response is why both constipation and diarrhea are listed as common effects when taking ferrous supplements.

The other options listed do not typically characterize the gastrointestinal effects of iron supplementation. Increased appetite and weight gain are not direct outcomes of taking iron supplements; rather, they might occur in certain clinical situations but are not primary effects. Headaches and dizziness could occur for a range of reasons related to iron levels but are not specifically gastrointestinal disturbances. Similarly, while nausea and heartburn can occur, they are more symptomatic of upper gastrointestinal distress rather than the direct actions on gut motility or stool consistency that characterize the correct choice.