Refers to the positive result or effectiveness of an action, effort, or treatment. Often used in phrases like 効がある (to be effective) or 効を奏する (to prove successful).
This medicine is effective for colds.
My efforts paid off and I passed the exam.
The steady effort paid off, and business performance recovered.
It can take several weeks for the effect of the treatment to show.
Once the medicine's effect wore off, the fever went up again.
効力 emphasizes the binding or legal potency of something (like a contract), while 効 refers more generally to a beneficial result of effort or treatment.
effect; effectiveness; result · effects (sound, visual, special)
valid; effective; in effect · yuko (judo)
efficiency
invalid; void; ineffective; unavailable
effect; efficacy; validity; potency
immediate effect; instant effect
statute of limitations; prescription; lapse of rights after a period of time · becoming invalid or void after a set time · ageing; aging
practical effect; efficacy; effective operation
effect; efficacy; benefit
The kanji 効 is composed of 交 (mix, intersect) and 力 (power), suggesting the idea of power being applied effectively. The reading こう is the on'yomi.
lapse; expiration; invalidation; becoming void
coming into effect; taking effect; becoming effective
use; utility; benefit; effectiveness
medical efficacy; effect of a medicine
striking effect; dramatic results; special efficacy · special effects; SFX
speedy effect; quick results; immediate action
delayed effect; delayed action
greenhouse gas
aftereffect; after effect
great effect; remarkable efficacy
efficacy; effectiveness
great efficiency; remarkable effectiveness
remarkable effect; miraculous efficacy
efficacy; effectiveness; taking effect
aftereffect
treatment efficacy; therapeutic effect
fertilizer response; effect of fertilizer