What occurs when the effectiveness of a drug diminishes over time with continued use?

The term that describes the phenomenon where the effectiveness of a drug diminishes over time with continued use is tolerance. Tolerance occurs when a person's response to a drug decreases after repeated use, which may lead them to require larger doses to achieve the same effect. This biological adaptation can occur due to various mechanisms, such as changes in receptor sensitivity or increased metabolism of the drug.

In the context of pharmacology, understanding tolerance is crucial for managing long-term treatment plans and ensuring patient safety. When tolerance develops, it can affect dosing regimens and therapeutic outcomes, necessitating careful monitoring by healthcare providers.

The other terms provided do not pertain to this specific phenomenon. Bioavailability refers to the proportion of a drug that enters systemic circulation and is available for activity, while an additive effect describes a scenario where two drugs together produce a combined effect that equals the sum of their individual effects. Peak level refers to the highest concentration of a drug in the bloodstream after administration. None of these concepts directly describe the diminishing effectiveness that occurs with persistent use of a drug.