Any dragon that failed to resist dragonbane was physically unable to enter the protected area for the duration of the spell. Spellcasting, breath weapons, or hurled objects were not prevented from crossing the barrier. The area of effect was a cube whose sides were the caster's level times 5 ft (1.5 m). Any dragons already within the area when the spell was cast were not affected by this spell unless they left the area and attempted to reenter. The duration of dragonbane was only a few minutes but could be extended greatly by use of a focus spell.