How is the term "tolerance" defined in pharmacology?

In pharmacology, "tolerance" refers specifically to a phenomenon where a patient requires higher doses of a drug to achieve the same therapeutic effect that was initially experienced at a lower dose. This adaptation occurs as the body becomes accustomed to the presence of the drug, leading to diminished effects over time. The mechanism behind this can involve a variety of physiological changes, such as receptor desensitization or changes in drug metabolism, but fundamentally, it underscores the importance of monitoring dosage levels in patients who have been on long-term medication regimens.

The other definitions, while pertinent to drug interactions and patient management, do not accurately capture the essence of tolerance. An increased response to a drug signifies sensitivity rather than tolerance. A patient's adverse reaction relates to side effects, and a temporary phase of medication adjustment does not signify a change in drug efficacy but rather the body's adaptation to a new regimen.