What is the adjectival form of efficacy? [closed]
Solution 1:
Effective is a common choice, or you may use the (slightly more highbrow) efficacious:
capable of or successful in producing an intended result; effective as a means, remedy, etc
I do not believe "efficate" would be well-understood.
Solution 2:
Conventionally, the adjectival form of efficacy is 'efficacious'. The adverb would be 'efficaciously'.