"The upper class of medicines.....govern the nourishment of destiny and correspond to heaven...., If one wishes to prolong the years of life without aging, one should" use these.
"The middle class of medicines govern the nourishment of one's nature and correspond to man. ...If one wishes to prevent illness and to supplement depletions and emaciations, one should" use these.
"The lower (class of) medicines....govern the treatment of illness and correspond to earth. If one wishes to remove cold, heat and (other) evil influences (from the body), to break accumulations, and to cure illnesses, one should base (one's efforts) on (drugs listed in) the lower (class of this) manual."
~ Shen Nong Ben Cao