Final answer:
Gingivitis option (B) is not a common side effect of iron preparations; black stools, constipation, diarrhea, nausea, and vomiting are more typical gastrointestinal responses to iron supplements.
Step-by-step explanation:
When taking iron preparations, side effects can include a variety of gastrointestinal issues. These side effects often consist of black stools, which is due to the iron content, and can range from constipation to diarrhea depending on how the individual's body reacts to the iron supplement. Additionally, people may experience general digestive discomfort including nausea or vomiting. However, gingivitis, which is inflammation of the gums, is not a common side effect of iron supplementation. Therefore, the correct answer to the question, 'When taking iron preparations, side effects can include all of the following except:', is B. gingivitis.