How is 'tolerance' defined in the context of drug use?

Tolerance is defined as the phenomenon where a person's reaction to a drug diminishes over time with prolonged use, leading to a decreased effect of the medication at the same dosage. As a result, to achieve the same effect, an individual may require higher doses of the drug. This process can occur due to various physiological adaptations, such as changes in receptor sensitivity or the body's increased efficiency in eliminating the drug.

In this context, the other options do not align with the definition of tolerance. Increased sensitivity to a drug's effects would describe a different interaction with the drug, enhancing its effect rather than diminishing it. Psychological dependence on a medication refers to a mental or emotional reliance on a drug, which is separate from the physical adaptations that characterize tolerance. Enhanced drug metabolism by the liver might play a role in the development of tolerance, but it is a specific mechanism rather than a definition of tolerance itself.