Which of the following substances is utilized in diet pills and over-the-counter medications for its stimulant effects?

The substance that is commonly utilized in diet pills and over-the-counter medications for its stimulant effects is ephedrine. Ephedrine is a compound derived from the Ephedra plant and is known to stimulate the central nervous system, which can lead to increased wakefulness and energy levels. Due to these stimulating properties, it has been used in weight loss products because it can raise metabolism and promote calorie burning.

While caffeine also has stimulant effects and is found in various dietary and beverage products, it is not as commonly associated with traditional diet pills as ephedrine. Tylenol, which contains acetaminophen, and aspirin, a non-steroidal anti-inflammatory drug (NSAID), are primarily used for pain relief and reducing inflammation rather than for their stimulant effects. Therefore, ephedrine is the more suitable choice when specifically considering substances known for their stimulating properties in the context of diet pills and medications.