The invention is related to N-carbamoylmethyl-4(R)-phenyl-2-pyrrolidone crystalline polymorphic forms and their production methods, as well as to the use of said polymorphic forms for pharmaceutical compositions manufacturing.Cette invention concerne des formes polymorphes cristallines de N-carbamoylméthyl-4(R)-phényl-2-pyrrolidone et leurs procédés de production, ainsi que l'utilisation de ces formes polymorphes pour la production de compositions pharmaceutiques.