Efficacious

1. adjective

   marked by qualities giving the power to produce an intended effect; -Aldous Huxley

   “written propaganda is less efficacious than the habits and prejudices...of the readers”

2. adjective

   producing or capable of producing an intended result or having a striking effect; -LewisMumford

   “an air-cooled motor was more effective than a witch's broomstick for rapid long-distance transportation”

   Similar: effective, effectual