This happens because the receptors to which the drug binds are saturated at a concentration lower than that produced by the dose you're taking. So basically eve

This happens because the receptors to which the drug binds are saturated at a concentration lower than that produced by the dose you're taking. So basically everything over 100mg/d is just going straight out via your kidneys, and you can taper down from whatever dosage to there in more or less whatever fashion you please because none of it has a meaningful effect on your brain chemistry in any case.