Three drugs are reacted with 2,4-dinitrophenyl hydrazine (2,4-DNPHz) in the presence of potassium periodate and sodium hydroxide to form colored products. The absorbance values for the formed complexes were measured at 403nm for olanzapine, 405nm for trifluoperazine hydrochloride, and 485nm for carbamazepine; against reagent blank. Different variables affecting the completion of the reaction have been carefully optimized by varying the parameters one at a time and controlling all others fixed. The results show better optical characteristics for calibration curve and statistical data under optimum conditions.