A drug is a substance that is used to treat, cure, or prevent a disease or medical condition. It can also refer to a substance that alters the way the body or mind functions. Caffeine is a stimulant drug commonly found in coffee, tea, and energy drinks. It affects the central nervous system, increasing alertness and reducing fatigue.
Note: The provided meaning of the answer is for the latest New York Times crossword puzzle clue: The "D" of F.D.A.. Explanations are generated by AI and may be inaccurate.