How do you spell Efficacy?
Correct spelling
efficacy
Think 'effective' with -acy ending: effi-CAC-y keeps the C from efficacious
Why is efficacy spelled this way?
From Latin efficacia, effectiveness. EX (out) + FACERE (to do). Efficacy is doing that produces results — effectiveness measured by outcomes.
Common misspellings of efficacy
efficencyeffecacyefficasyefficicity
Example
The new medication's efficacy was proven through rigorous clinical trials.