Feeblemind

The insidious feeblemind spell affects only those who can cast spells, tracing and poisoning the mystical channels of their arcane power like a viral infection. The spell reduces a victim into a state of extreme mental retardation, which condition persists until the victim is magically restored by means of a heal, wish, or restoration spell. The different types of spell casting ability are not equally vulnerable to the feeblemind spell. Practitioners of clerical magic gain a bonus of +1 to saving throws; druids save at –1; magic users and illusionists save at –4. (Those who can use more than one type of magic must save using the average of their modifiers.)