On the point of being held liable for prescribing medicines that are available over the counter...I was told by a professor of medical law that, for example, if someone complains of a headache and a lay person suggests two asprin, it is not the same as your neighbor the nurse suggesting the same two asprin. In the case of the nurse, advanced medical knowledge is implied and the advice, therefore, carries more weight. You think you can trust the nurse to know what's good for you in that situation and perhaps act according with that trust. Theoretically, if the headache were from something serious that needed other intervention which was delayed because of the nurse's advice, s/he would be liable. Hope this helps with that small part of the question.