Efficacy

Efficacy is the capacity for beneficial change (or therapeutic effect) of a given intervention, most commonly used in the practice of medicine and pharmacology.

Medicine

In medicine, efficacy is the capacity for beneficial change (or therapeutic effect) of a given intervention (for example a drug, medical device, surgical procedure, or a public health intervention). If efficacy is established, an intervention is likely to be at least as good as other available interventions, with which it will have been compared. Comparisons of this type are typically made in 'explanatory' randomized controlled trials, whereas 'pragmatic' trials are used to establish the effectiveness of an intervention.

When talking in terms of efficacy vs. effectiveness, effectiveness relates to how well a treatment works in the practice of medicine, as opposed to efficacy, which measures how well treatment works in clinical trials or laboratory studies.

Pharmacology

In pharmacology, efficacy (E_max) is the maximum response achievable from a drug.Intrinsic activity is a relative term that describes a drug's efficacy relative to a drug with the highest observed efficacy. Effectiveness refers to the ability of a drug to produce a beneficial effect. A distinction is made between 'method' effectiveness which describes the effect achievable if the drug was taken as prescribed and 'use' effectiveness which is the effect obtained under typical use circumstances when adherence is not 100%. The widely used intention to treat method of analysing clinical trials provides estimates of 'use' effectiveness which are typically biased compared with 'method' effectiveness. Efficacy is the magnitude of response with respect to the K_d.