The rod of withering acts as a +1 light mace that deals no hit point damage. Instead, the wielder deals 1d4 points of temporary Strength damage and 1d4 points of temporary Constitution damage to any creature she touches with the rod (by making a melee touch attack). If she scores a critical hit, the damage from that hit is actually permanent ability drain. In either case, defender negates the effect with a Fortitude save (DC 14).