What is an example of tolerance in pharmacology?

In pharmacology, tolerance refers to a physiological state where a person's reaction to a drug diminishes over time, often requiring higher doses to achieve the same effect that was previously attained with a lower dose. The correct answer highlights this concept, as when a drug loses its effect after prolonged use, this indicates that the body has adapted to the presence of the drug. As a result, the individual may need to increase the dosage to experience the initial therapeutic effects, which exemplifies the development of tolerance.

Other options represent different phenomena. An immediate allergic reaction typically involves the immune system responding adversely to a drug, not a gradual change in response. Elevation of drug dosage without effects does not fit the typical understanding of tolerance as it suggests that increasing the dose has no impact, which doesn't align with the concept. A sudden adverse reaction after first use is indicative of sensitivity or an allergic reaction rather than tolerance, as no prior exposure exists to develop a tolerance.