Nouns ending in a consonant followed by -y change the -y to -ies in the plural form.
Efficacy is regular. It follows the -ies Conversion rule.
Use plural verbs: "The efficacies are ready" (not "is ready").
Yes. The plural efficacies is standard across all English variants.
The word efficacy follows the standard English pluralization rule. When forming the plural, efficacy becomes efficacies. This follows the -ies Conversion pattern, which is one of the most common plural rules in English.
Understanding why efficacy becomes efficacies helps with spelling and pronunciation. Nouns ending in a consonant followed by -y change the -y to -ies in the plural form.
When using efficacies in writing, remember that it functions as a plural noun in sentences. It pairs with plural verbs and pronouns. For example: "The efficacies are ready" (not "is ready"). This subject-verb agreement is essential for grammatical correctness.