Perhaps the answer is there is no answer. When I taught children with a variety of problems. my principal used to tell me, don't look for reasons or names, deal with the symptoms themselves. Vicodin doesn't do anything for me (No pain relef or high or sleepy), yet Advil (OTC) does relieve pain. Evderyone is so different. As my psychotic student would say after he stole a teacher's reading workbook answer book, " Answers may vary" for some questions.