For restoration shamans, the Cleanse Spirit spell completely replaces this spell. It costs the same amount of mana and removes one curse effect in addition to the disease and/or poison.
Consider using Cleansing Totem instead. It has the same mana cost or less if you have Totemic Mastery and will retry every 5 seconds for five minutes, however your target must be in your party, within 30 yards, and you will lose any other water totem you have out. If more than one person in your group are diseased or poisoned, it is usually faster and cheaper to use Cleansing Totem and then immediately replace it with the water totem you had up before. The reduced global cooldown on totems means that this 'totem switch' will only take two seconds, whereas casting Cure Disease twice takes three seconds.
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Patch 4.0.1 (2010-10-12): Removed. 
