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 1
  • Pharmacology 2
  • See also 3
  • References 4


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, to 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.[1]


In pharmacology, efficacy (Emax) is the maximum response achievable from a drug.[2] 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 Kd.

See also


  1. ^ How FDA Approves Drugs see textbox pg 4. There is some confusion caused by the fact that the FDA has a mandate to insure that drugs are "safe and effective," but in reality the FDA will approve drugs that have been proven to have clinical efficacy, without any of the required proof of "clinical effectiveness" by this definition.
  2. ^ Holford NHG, Sheiner LB. Understanding the dose-effect relationship: clinical application of pharmacokinetic-pharmacodynamic models. Clin Pharmacokinet. 1981;6(6):429-53.