Reduce person was a transmutation spell that was the counter to enlarge person. This was the only version that was considered a separate spell for the purposes of adding it to a spellbook—all others were considered facets of their corresponding enlarge spells. (See enlarge or reduce person.)
Unless the subject resisted, this spell instantly caused the target humanoid creature to shrink to half-size in all three dimensions and correspondingly weigh one-eighth of their original weight. This change generally made the target more dexterous and harder to hit, but also made them weaker and reduced their reach. All clothing, equipment, and carried items shrank proportionately, but any item that was dropped, thrown, or shot immediately returned to original size and weight upon leaving the reduced person's possession.
A creature already under the influence of this or any other reduction spell was immune to another application of this or any other reduction spell. Reduce person countered and was countered by the transmutation version of enlarge person.