I don't have an answer for you. I'm not sure how things work in this situation, but I know I've learned to trust my daughter when she says she doesn't feel "right". She can sense some kind of a difference (usually involving a headache, sometimes dizziness, sometimes other things) and she will tell me that she needs more meds. I'll give her an extra pill... sometimes two, then she lays down for awhile and later on she feels fine.