What is Efficacy?

In medical terms, efficacy refers to the ability of a product or treatment to provide a beneficial effect.

Image Credit: Wanannc / Shutterstock
Image Credit: Wanannc / Shutterstock


In the context of healthcare, the efficacy of a product to yield therapeutic benefits is explored. Interventions that may be explored include drugs, medical devices, surgical procedures and public health interventions

The intervention is compared to other interventions available at the time and efficacy is established if the new intervention is at least as good as the others available. Typically, these types of comparisons are made in randomized clinical trials.


In pharmacology, efficacy describes the maximum response that can be achieved with a drug. The effect of the drug is plotted against dose in a graph, to give the dose–response curve. The increasing doses used are displayed by the X axis and the half maximal and maximal responses are displayed by the Y axis. The highest point on the curve shows the maximum response (efficacy) and is referred to as the Emax.

The effectiveness of a drug is considered in two distinct ways, “method effectiveness” and “use” effectiveness.

Method effectiveness refers to the maximum response that is achieved when the drug is taken exactly as prescribed, while use effectiveness describes the response obtained when the drug is used under typical circumstances, when adherence to the drug may not be 100%.

The use effectiveness which is typically assessed during “intention to treat” analysis of clinical studies is often biased compared to the findings obtained when method effectiveness is used.

Further Reading

Last Updated: Feb 1, 2021

Dr. Ananya Mandal

Written by

Dr. Ananya Mandal

Dr. Ananya Mandal is a doctor by profession, lecturer by vocation and a medical writer by passion. She specialized in Clinical Pharmacology after her bachelor's (MBBS). For her, health communication is not just writing complicated reviews for professionals but making medical knowledge understandable and available to the general public as well.


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  1. Mandy Scott Mandy Scott United Kingdom says:

    Is there anyone out there, or knows of any clinical trials for metastasis prostrate cancer,
    So very desperate to extend my son- in-laws life,we are praying for him to have extra time. 6th cycle of chemotherapy today and his PSA is increasing dramatically, gone up to 47 since he started his 1st cycle. He’s hormone resistance, had radiation therapy and been told that his chemotherapy is to prolong life. Someone please please help

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