What is defined as a substance taken to treat or prevent disease?

The correct response is medication. Medication refers specifically to substances that are designed to treat, prevent, or diagnose diseases or medical conditions. These can include both prescription and over-the-counter products that have a therapeutic purpose.

The term "drug" may seem relevant, as it also refers to substances used for medical treatment. However, in this context, medication is the more precise term, as it encompasses a wide range of medicinal products specifically formulated for patient care, whereas the term "drug" may also refer to illegal substances or recreational drugs, which do not fit the definition of being taken to treat or prevent disease.

Both vitamins and supplements typically serve a supportive role in health maintenance but are not primarily classified as treatments for disease. They may have health benefits, but they do not replace medications prescribed for medical conditions. Thus, medication stands as the most accurate choice here, clearly indicating its role in healthcare and disease management.