"I would fear infinitely if they lost or exchanged their labels, reversing their regions," the 16th-century French thinker Michel de Montaigne stated, referring to the various medicines a patient was taking. It was an interesting concern from a visionary, because centuries later, drugs that don't reach the correct part of the body or that interact with other parts of the body still cause problems. This is one of the causes of drug side effects or their lack of effectiveness.