Which of the following substances is considered a drug?

A substance intended for use in diagnosis is considered a drug because it is specifically designed to prevent, treat, or alleviate symptoms of a disease or condition. This aligns with the definition of a drug under the law, which includes any substance used for the purpose of diagnosis, cure, mitigation, treatment, or prevention of disease in humans or animals.

In contrast, the other options do not meet the criteria to be classified as a drug. Food products are primarily intended for nourishment and do not have the same therapeutic purposes as drugs. A non-food article that has no health impact does not serve a medical use and therefore cannot be considered a drug. Finally, while cosmetic products may have benefits for appearance and may impact health in some way, their primary purpose is not to diagnose or treat medical conditions but to enhance beauty. Thus, only the substance intended for use in diagnosis fits the definition of a drug.