I already answered why, it's chemistry. Everyone has side effects, not everyone notices them. You can not introduce a medication, or any substance for that matter, into the human body that does not have any side effects — it's impossible.
Normally when people say side effects they mean things that you can actually observe. Hence your earlier point about going off the meds and noticing a difference. If I don't notice any difference other than I don't think your point really stands.
