Efficacy vs Efficiency

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What’s the difference between them?



The ability to produce a desired or intended result.


1. The efficacy of the new medicine has been proven successful in clinical trials.

2. The efficacy of the program is undeniable, as the results have been overwhelmingly positive.

3. We must continue to evaluate the efficacy of the vaccine to ensure its safety.



The quality of achieving maximum productivity with minimum wasted effort or expense.


1. Working from home has greatly improved my efficiency.

2. The new software helped to increase the efficiency of the production line.

3. I was impressed by her efficiency when completing the task.

Learn similar and opposite words to spot the difference




1. Effectiveness

2. Productivity

3. Capability

4. Proficiency

5. Competence

1. Ineffectiveness

2. Inability

3. Mediocrity

4. Incompetence

5. Unsuccessfulness


1. Proficiency

2. Efficiency

3. Competence

4. Productiveness

5. Accomplishment

1. Inefficiency

2. Lethargy

3. Disorganization

4. Sloppiness

5. Wastefulness

Tricks for mastery

Useful tips to understand the difference between confusing words "Efficacy", "Efficiency".

1. Efficacy is about effectiveness, efficiency is about productivity.

2. Efficacy refers to the ability to achieve desired results, while efficiency is focused on conserving resources and minimizing costs.

3. Efficacy measures results in terms of accuracy and performance, while efficiency measures results in terms of time and resources used.

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Frequently asked questions

In what situations should the word 'Efficacy' be used?

Efficacy is typically used in the context of health care, to refer to a treatment's ability to produce a beneficial result or outcome. In general, efficacy is used to describe how effective something is in achieving a desired result.

When is the appropriate context for using the word 'Efficiency'?

Efficiency is typically used to refer to how effectively something is done with the least amount of wasted time and resources. It is often used to refer to the performance of a system, process, or machine.

Do the two words share the same pronunciation?

No, the two words have different pronunciations. Efficacy is pronounced 'eh-fih-kuh-see' and efficiency is pronounced 'ih-fish-uhn-see'.

What are some common mistakes people make when using these words?

The main mistake people make when using these two words is confusing them. Another mistake is to use 'efficacy' when referring to how efficiently something is done, and 'efficiency' when referring to how effectively it produces a result. Both words have unique definitions and should be used with care.

Fill in the gaps to check yourself

1. The ____ of the new drug was remarkable, making it more efficient than any of its predecessors.

2. We must strive to increase efficacy without sacrificing ____.

3. After an extensive review, the board determined that ____ should be prioritized over efficiency.

4. Despite its ____, the process was not particularly efficient.

5. Through a combination of efficiency and ____, the team was able to achieve a positive outcome.

6. Although the task required a high degree of efficacy, ____ was key to its successful completion.

1. Efficacy

Explanation: The term efficacy refers to the actual effectiveness of the drug in achieving its intended purpose. Efficiency describes how well the drug is able to achieve its purpose while using fewer resources.

2. Efficiency

Explanation: Efficiency refers to the ability to do something with the least amount of effort or resources. In this case, it refers to achieving the desired result without sacrificing the effectiveness of the drug.

3. Efficacy

Explanation: The board determined that the drugs effectiveness and ability to achieve its desired purpose should be prioritized over its ability to achieve the same results with fewer resources.

4. Efficiency

Explanation: Despite the drugs effectiveness, the process of using it was not as efficient as it could be, meaning it was not as effective in using fewer resources.

5. Efficacy

Explanation: Through a combination of the drugs effectiveness and the teams ability to use fewer resources, they were able to achieve a positive outcome.

6. Efficiency

Explanation: Although the task required a high degree of effectiveness, it was also important that the team was able to complete it in an efficient manner, using fewer resources.

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List of Commonly Confused Words

Finding your way around the English language can be hard, especially since there are so many confusing words and rules. So, a list of the most confusing words in English is an extremely useful tool for improving language accuracy and sharing the ideas clearly.