What measurement indicates how well a medication works?

The measurement that indicates how well a medication works is indeed drug effectiveness. This term broadly encompasses the ability of a drug to produce a desired therapeutic effect in patients when used under normal circumstances. Drug effectiveness can be assessed through clinical trials and real-world observations, often measured by comparing outcomes such as symptom relief, changes in disease progression, or overall patient health when using the medication.

Evaluating drug effectiveness is essential because it informs healthcare providers about how well a treatment is likely to perform in different populations or settings, and helps guide clinical decisions.

In contrast, the therapeutic index is a measure of the safety margin of a drug, indicating the difference between effective doses and toxic doses, but does not directly assess its efficacy. Tolerability refers to the side effects and the degree to which a patient can tolerate them, and compliance rate pertains to how consistently patients take their medication as prescribed. While these factors are important in the overall assessment of a medication's use in practice, they do not specifically indicate how well the medication achieves its intended therapeutic effect.