Medicine is anything that which raises the spirits and makes a person feel better, using the broader, native American use of the word. The native Americans, like other human groups living close to the earth, have a clearer, less cluttered view of themselves and the world around them.
The close relationship between one's state of mind, specifically one's state of happiness, and one's physical health is seen clearly by native people. Anything seen to positively impact the spirit of the person is also seen to positively impact the health of the body. Therefore all these things are called medicine, not just those things that act specifically on the body.
In our society the word medicine is more narrow in meaning and reflects our narrower view of what it means to be a healthy human being. We are overly focused on the body and have largely forgotten the role one's spiritual well-being has in keeping us fit, healthy and free of disease.