This medicine's dosage will vary depending upon individual to individual. Take your doctor's instructions or the label's directions. Modafinil is used to treat extreme drowsiness in individuals who have narcolepsy, either with or without cataplexy. Excessive drowsiness is described as trouble staying awake and a higher chance of falling asleep at unexpected places. Just the usual dosages of this drug are included in the information. If you want to change the dosage, do not alter it unless your physician instructs you to.