efficacious adj 1: marked by qualities giving the power to produce an intended effect; "written propaganda is less efficacious than the habits..."
1. effective means 'having a (desired) result or effect,' effectual is 'succeeding in producing a desired result or effect,' and efficacious means the same as effectual as well as 'serving as an effective solution or remedy'
2. if something is efficacious, it is able to produce the desired result; efficacy means the power to produce effects
efficacious - Synonyms from Thesaurus.com
The sisters’ reprimand was efficacious; Rachel left her sorority house in tears, and refused to eat for an entire week.
The most efficacious medical cocktail prescribed to Janet was also the most pleasure inducing and life shattering.
mental_floss Vocab Rehab » efficacious (adj.)