Please note: The term 'efficacy' has a specific definition when used by drug licensing companies.

TU, Germany

The terms “effectiveness” and “efficacy” seem to be used as synonyms and to be quite interchangeable, despite formal conceptual differences between both. To my knowledge this might be due to translation difficulties (in German for example “Efficacy” is usually translated as “Wirksamkeit” and “Effectiveness” as “Wirksamkeit unter Alltagsbedingungen”, which is then too often shortened leaving “Wirksamkeit” alone again). The confusion might be also due to lack of clarity on interpreting whether the conditions of a trial were so far a way from conditions in every day practice.

Servicio de Evaluacion y Planificacion, Canary Islands

In a medical context it indicates that the therapeutic effect for a given intervention (e.g. intake of a medicine, an operation, or a public health measure) is acceptable. Efficacy in this context refers to a consensus that it is at least as good as other available interventions to which it will have ideally been compared to in a clinical trial. For example, an efficacious vaccine has the ability to prevent or cure a specific illness in an acceptable proportion of exposed individuals.


Efficacy is the extent to which a specific intervention, programme or service produces a beneficial result under ideal conditions. The definition of ideal conditions is based on the results of a randomized controlled trial.

Effectiveness is the extent to which a specific intervention, programme or service, when developed in the field, does what it is intended to do for a defined population.

NOKC, Norway

Efficacy refers to the trial setting, and thus any HTA need to consider whether the results obtained in clinical trials can be generalized outside to clinical practice. In some instances “real world” studies are conducted to evaluate real world effectiveness, such studies are however often registry based and thus not of a design comparable to study designs most often included to analyse efficacy.

Editor of Clinical Guidelines, Directorate of Health, Iceland


Describes how well or badly some input (intervention/ health technology like drugs, screening program etc) works under ideal circumstances whether artificial (research setting) or natural (created by for example geography, captive population).


Describes how well or badly some input (specific interventions / health technology like drugs, screening program or other services etc) works under usual circumstances (real world or usual practice).

HTA Agency, Poland

Effectiveness and Efficacy

As for Effectiveness and Efficacy, we do not think, that there can be problem with mistaking this two terms.

As “Efficacy” refers strictly to the trial setting it is difficult to even assume to what extent, the effects obtained in such “ideal” setting can be generalized outside to clinical practice, where the conditions as well as characteristics of treated population differs.

INAHTA Glossary

Effectiveness: The benefit (e.g. to health outcomes) of using a technology for a particular problem under general or routine conditions, for example, by a physician in a community hospital or by a patient at home.