Efficacy is the ability to perform a task to a satisfactory or expected degree. The word comes from the same roots as ''

effectiveness Effectiveness or effectivity is the capability of producing a desired result or the ability to produce desired output. When something is deemed effective, it means it has an intended or expected outcome, or produces a deep, vivid impression. Et ...

'', and it has often been used synonymously, although in

pharmacology Pharmacology is the science of drugs and medications, including a substance's origin, composition, pharmacokinetics, pharmacodynamics, therapeutic use, and toxicology. More specifically, it is the study of the interactions that occur betwee ...

a distinction is now often made between efficacy and effectiveness. The word ''efficacy'' is used in

and

medicine Medicine is the science and Praxis (process), practice of caring for patients, managing the Medical diagnosis, diagnosis, prognosis, Preventive medicine, prevention, therapy, treatment, Palliative care, palliation of their injury or disease, ...

to refer both to the maximum response achievable from a

pharmaceutical drug Medication (also called medicament, medicine, pharmaceutical drug, medicinal product, medicinal drug or simply drug) is a drug used to diagnose, cure, treat, or prevent disease. Drug therapy ( pharmacotherapy) is an important part of the ...

in research settings, and to the capacity for sufficient therapeutic effect or beneficial change in clinical settings.

Pharmacology

In pharmacology, efficacy () is the maximum response achievable from an applied or dosed agent, for instance, a small molecule drug.

Intrinsic activity Intrinsic activity (IA) and efficacy (Emax) refer to the relative ability of a drug- receptor complex to produce a maximum functional response. This must be distinguished from the affinity, which is a measure of the ability of the drug to bind ...

is a relative term for a drug's efficacy relative to a drug with the highest observed efficacy. It is a purely descriptive term that has little or no mechanistic interpretation. In order for a drug to have an effect, it needs to bind to its target, and then to affect the function of this target. The target of a drug is commonly referred to as a

receptor Receptor may refer to: * Sensory receptor, in physiology, any neurite structure that, on receiving environmental stimuli, produces an informative nerve impulse *Receptor (biochemistry), in biochemistry, a protein molecule that receives and respond ...

, but can in general be any chemically sensitive site on any molecule found in the body. The nature of such binding can be quantified by characterising how tightly these molecules, the drug and its receptor, interact: this is known as the

affinity Affinity may refer to: Commerce, finance and law * Affinity (law), kinship by marriage * Affinity analysis, a market research and business management technique * Affinity Credit Union, a Saskatchewan-based credit union * Affinity Equity Pa ...

. Efficacy, on the other hand, is a measure of the action of a drug once binding has occurred. The maximum response, , will be reduced if efficacy is sufficiently low. The definition of efficacy has been object for discussion. The only way in which absolute measures of efficacy have been obtained is by single ion channel analysis of ligand gated ion channels. It is still not possible to do this for G protein-linked receptors. In the case of the glycine receptor and the nicotinic acetylcholine receptor (muscle type), it has been proposed by Sivilotti ''et al''. that opening of the ion channel involves two steps after agonist is bound. Firstly a conformation change to a higher affinity (but still shut) form, followed by the conformation change from shut to open. It was found that partial agonism results from deficiency in the first step, and that the opening and shutting steps are essentially the same for both full and partial agonists. This has been confirmed and extended by Sine and colleagues (2009). The implication of this work is that efficacy has to be defined by at least two equilibrium constants (or, more generally, by four rate constants). The combined influences of affinity and efficacy determine how effectively a drug will produce a biological effect, a property known as

potency Potency may refer to: * Potency (pharmacology), a measure of the activity of a drug in a biological system * Virility * Cell potency, a measure of the differentiation potential of stem cells * In homeopathic dilutions, potency is a measure of ho ...

Medicine

In medicine, efficacy is the capacity for beneficial change (or

therapeutic effect Therapeutic effect refers to the response(s) after a treatment of any kind, the results of which are judged to be useful or favorable. This is true whether the result was expected, unexpected, or even an unintended consequence. An adverse effect (i ...

) of a given intervention (for example a drug,

medical device A medical device is any device intended to be used for medical purposes. Significant potential for hazards are inherent when using a device for medical purposes and thus medical devices must be proved safe and effective with reasonable assura ...

surgical procedure Surgery is a medical specialty that uses manual and instrumental techniques to diagnose or treat pathological conditions (e.g., trauma, disease, injury, malignancy), to alter bodily functions (e.g., malabsorption created by bariatric surgery s ...

, or a

public health Public health is "the science and art of preventing disease, prolonging life and promoting health through the organized efforts and informed choices of society, organizations, public and private, communities and individuals". Analyzing the de ...

intervention). Establishment of the efficacy of an intervention is often done relative to other available interventions, with which it will be compared. Specifically, efficacy refers to "whether a drug demonstrates a health benefit over a placebo or other intervention when tested in an ideal situation, such as a tightly controlled clinical trial." These studies focus on a primary parameter to be shown statistically different between placebo and intervention groups. Comparisons of this type are called 'explanatory'

randomized controlled trial A randomized controlled trial (or randomized control trial; RCT) is a form of scientific experiment used to control factors not under direct experimental control. Examples of RCTs are clinical trials that compare the effects of drugs, surgical ...

s, whereas 'pragmatic' trials are used to establish the ''effectiveness'' of an intervention regarding also non-specific parameters. Effectiveness refers to "how the drug works in a real-world situation", and is "often lower than efficacy because of interactions with other medications or health conditions of the patient, sufficient dose or duration of use not prescribed by the physician or followed by the patient, or use for an off-label condition that had not been tested."

Agriculture

In agriculture and forestry, efficacy is used to describe whether a

pesticide Pesticides are substances that are used to control pests. They include herbicides, insecticides, nematicides, fungicides, and many others (see table). The most common of these are herbicides, which account for approximately 50% of all p ...

is effective in controlling a pest or disease.

Theology

Scripture

Protestant Theology Protestant theology refers to the doctrines held by various Protestant traditions, which share some things in common but differ in others. In general, Protestant theology, as a subset of Christian theology, holds to faith in the Christian Bible, t ...

(esp. in

Lutheran Lutheranism is a major branch of Protestantism that emerged under the work of Martin Luther, the 16th-century German friar and Protestant Reformers, reformer whose efforts to reform the theology and practices of the Catholic Church launched ...

but also in

Calvinist Reformed Christianity, also called Calvinism, is a major branch of Protestantism that began during the 16th-century Protestant Reformation. In the modern day, it is largely represented by the Continental Reformed Protestantism, Continenta ...

doctrine) ''efficacy'' is an attribute of

Scripture Religious texts, including scripture, are texts which various religions consider to be of central importance to their religious tradition. They often feature a compilation or discussion of beliefs, ritual practices, moral commandments and ...

. The efficacy of Scripture means that it is united with the power of the Holy Spirit and with it, not only demands, but also creates the acceptance of its

teaching Teaching is the practice implemented by a ''teacher'' aimed at transmitting skills (knowledge, know-how, and interpersonal skills) to a learner, a student, or any other audience in the of an educational institution. Teaching is closely related ...

and that this teaching produces faith and

obedience Obedience, in human behavior, is a form of "social influence in which a person yields to explicit instructions or orders from an authority figure". Obedience is generally distinguished from compliance, which some authors define as behavior infl ...

. Efficacy further means that Holy Scripture is not a dead letter, but rather, the power of the Holy Spirit is inherent in it and that Scripture does not compel a mere intellectual assent to its doctrine, resting on logical argumentation, but rather it creates the living agreement of faith. The

Smalcald Articles The Smalcald Articles or Schmalkald Articles () are a summary of Lutheran doctrine, written by Martin Luther in 1537 for a meeting of the Schmalkaldic League in preparation for an intended ecumenical Council of the Church. History The Schmalkaldi ...

affirm, "in those things which concern the spoken, outward Word, we must firmly hold that God grants His Spirit or grace to no one, except through or with the preceding outward Word." The

Formula of Concord Formula of Concord (1577) (; ; also the "''Bergic Book''" or the "''Bergen Book''") is an authoritative Lutheran statement of faith (called a confession, creed, or "symbol") that, in its two parts (''Epitome'' and ''Solid Declaration''), makes up ...

teaches that when humans reject the calling of the Holy Spirit, it is not a result of the Word being less efficacious. Instead, contempt for the

means of grace The means of grace in Christian theology are those things (the ''means'') through which God gives grace. Just what this grace entails is interpreted in various ways: generally speaking, some see it as God blessing humankind so as to sustain and em ...

is the result of "the perverse will of man, which rejects or perverts the means and instrument of the Holy Ghost, which God offers him through the

call Call or Calls may refer to: Arts, entertainment, and media Games * Call (poker), a bet matching an opponent's * Call, in the game of contract bridge, a bid, pass, double, or redouble in the bidding stage Music and dance * Call (band), from L ...

, and resists the Holy Ghost, who wishes to be efficacious, and works through the

Word A word is a basic element of language that carries semantics, meaning, can be used on its own, and is uninterruptible. Despite the fact that language speakers often have an intuitive grasp of what a word is, there is no consensus among linguist ...

..."

Prayer

References

{{Pharmacology Medical terminology Pharmacodynamics