• Today's Word

Efficacious

🔊 Listen to the word Efficacious

ef-ih-KAY-shus

Definition

(adjective) Capable of producing the desired result; successful in achieving the intended outcome.

Example

The new treatment proved remarkably efficacious in clinical trials, reducing symptoms in over ninety percent of patients within the first two weeks.

Word Origin

Efficacious derives from the Latin efficax, meaning “powerful” or “effectual,” rooted in efficere — “to bring about” or “to accomplish” — built from ex- (“out”) and facere (“to make” or “to do”). The same root gives us effect, efficient, and efficacy — a family of words all built around the idea of something being done and producing a result. It entered English in the 16th century, used predominantly in medical and philosophical contexts to describe remedies or arguments that actually worked.

Fun Fact

The history of medicine is largely a history of distinguishing the efficacious from the merely plausible. For centuries, bloodletting was considered one of the most efficacious treatments available — practiced by physicians from ancient Greece through the 19th century for conditions ranging from fever to mental illness. George Washington died in 1799 partly as a result of aggressive bloodletting performed by his own doctors in response to a throat infection. It wasn’t until the rise of controlled clinical trials in the 20th century that medicine developed reliable tools for separating treatments that actually worked from treatments that merely seemed to — a distinction efficacious had been waiting two thousand years for medicine to catch up with.