Efficacy
/ˈɛfɪkəsi/
nounC1
Definition
Efficacy is the power or ability of a thing (like a medicine, plan, or method) to work well and achieve the result it is supposed to. It shows how effective or successful something is in doing what it should do.
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See It in Action
The ability of something to produce the intended result
- •The efficacy of the new drug was proven in clinical trials.
- •Researchers studied the efficacy of different teaching methods.
- •The vaccine showed high efficacy in preventing the disease.
Make It Stick
- ✓Think of "efficacy" like "success," but it focuses on how well something works, not just if it happens
- ✓Picture a medicine curing a patient—its efficacy is how well it heals the illness
- ✓It's the feeling of confidence when you know a tool or plan will work as expected
- ✓Sounds like "effi-CA-cy" → imagine a powerful "efficient" machine that always completes its job perfectly
- ✓Remember a teacher testing a new method and seeing if students learn better—that shows the method's efficacy
- ✓NOT like "efficiency" (how fast or with little waste)—efficacy is about the result, not speed or cost
- ✓NOT like "effectiveness" (very close meaning), but efficacy is often used in formal or scientific contexts
- ✓NOT like "success" (which is broad)—efficacy is about producing the correct or wanted effect specifically
Try Other Words
- •Effectiveness: how well something works (Use when talking more generally about results in everyday language)
- •Power: ability to do something (Use when emphasizing strength or force)
- •Performance: how well something works or functions (Use when focusing on activity or operation)
Unboxing
- •Word parts: "effic-" (from Latin "efficere" meaning to bring about or accomplish) + suffix "-acy" (forms nouns showing quality or state)
- •Etymology: From Latin "efficacia," meaning the power to produce an effect
- •Historical development: Entered English in the 1600s, mostly used in formal, scientific, or medical language
- •Modern usage: Common in medicine, science, and research to describe how well treatments or methods work
Reflect & Connect
•How can understanding efficacy help you decide which medicines or methods to trust?
•Can something have high efficacy but still fail in real life? Why might that happen?
Fill in the blanks
1.The efficacy of the medicine depends on ___ the correct dose is given.
2.Scientists measure efficacy to see if a treatment can ___ the disease.
3.Unlike efficiency, efficacy focuses on the ___ of the result, not the speed or cost.
4.The new teaching method showed great efficacy in helping students ___ their skills.
5.Sometimes a plan has good efficacy in tests but fails because people ___ it correctly.
6.Efficacy is important when deciding which vaccine to ___ in a health program.
7.The study compared the efficacy of two drugs to find out which one ___ better results.