Might we not be doing huge self medication by taking supplements ?

You are correct: Thankfully, most of them are placebos or have relatively mild biologic effects. A couple of the botanicals are extremely dangerous and only politics-as-usual keeps them legal in the usa. Some are quite helpful -- just tonight, i've recommended asking a personal physician about yohimbine. And vegetarians do need to supplement or they get multiple deficiencies -- otherwise the lifestyle's great.