What does the term "drug tolerance" refer to?

The term "drug tolerance" specifically refers to a state where a patient experiences a reduced response to a drug after its prolonged use. As a result, the patient may require higher dosages to achieve the same therapeutic effect that was previously attained with a lower dosage. This phenomenon occurs because the body becomes accustomed to the presence of the drug, leading to decreased sensitivity over time.

In the context of the other provided options, heightened sensitivity to a medication’s effects describes a different situation where the body reacts more strongly rather than less to a drug. An allergic reaction involves the immune system responding adversely to a medication, distinguishing it from the concept of tolerance, which is more about the pharmacological response over time. Lastly, combining two different drugs for enhanced effect addresses polypharmacy and drug interaction rather than the process of developing tolerance to a single medication. Hence, the answer accurately captures the essence of what drug tolerance entails.