Er ikke lige hjemme men her er hvad jeg kunne finde på nettet:
From the Saving Throw section on pages 171 and 172 of the Player's Handbook:
Stacking Effects: Spells that provide bonuses or penalties on attack rolls, damage rolls, saving throws, and other attributes usually do not stack with themselves. For example, two bless spells don't give twice the benefit of one bless. Both bless spells, however, continue to act simultaneously, and if one ends first, the other one continues to operate for the remainder of its duration. Likewise, two haste spells do not make a creature doubly fast. More generally, two bonuses of the same type don't stack even if they come from different spells (or from effects other than spells; see Bonus Types, above). For example, the enhancement bonus to Strength from a bull's strength spell and the enhancement bonus to Strength from a divine power spell don't stack. You use whichever bonus gives you the better Strength score. In the same way, a belt of giant Strength gives you an enhancement bonus to Strength, which does not stack with the bonus you get from a bull's strength spell.
Same Effect More than Once in Different Strengths: In cases when two or more identical spells are operating in the same area or on the same target, but at different strengths, only the best one applies. For example, if a character takes a -4 penalty to Strength from a ray of enfeeblement spell and then receives a second ray of enfeeblement spell that applies a -6 penalty, he or she takes only the -6 penalty. Both spells are still operating on the character, however. If one ray of enfeeblement spell is dispelled or its duration runs out, the other spell remains in effect, assuming that its duration has not yet expired.
Så nej, de stacker ikke...hvis det altså er rigtig afskrevet af den person den skrev det på nettet.