needing and using much energy and thought

difficult, hard to endure

needing a lot of (mental or physical) effort

demanding

severe

severe, painful; serious

needing much effort

difficult; requiring hard labor

using or needing great effort

difficult; requiring hard work

causing worry, unhappiness, difficulty

bothersome, worrisome

causing tiredness, exhaustion, impatience etc

difficult, bothersome

causing worry

troublesome