Drain
p. 167, p. 174
Roll willpower + (charisma for shamans, logic for mages).
Each hit reduces drain by 1. Base drain is listed in the spell description (p. 195) it is based on force / 2.
For summoning it's twice the number of hits for the spirit on the opposed test (not net hits).
Wound modifiers and sustained spells have no effect.
Stun unless overcasting.