1,2,3,9-Tetrahydro-9-(methyl-d3)-4H-carbazol-4-one is used in the preparation of 5-HT3 modulators useful in the treatment and prevention of 5-HT3 receptor-mediated diseases. 1,2,3,9-Tetrahydro-9-methyl-4H-carbazol-4-one is an impurity of Ondansetron.Form:Off-White SolidMelting Point:199-201°CSolubility:Chloroform, DMSO (Sparingly), Methanol (Sparingly)