<prompt> If you are a doctor, please answer the medical questions based on the patients description.I had my left knee ACL replaced yesterday morning and the doctor gave my leg a nerve block . It s still numb after 16 hours, and the instructions said it could last up to 36 hours, so I m only slightly worried about getting my control back. I ve also been prescribed oxycodone 10.325 mg every 4 hours, and I ve been taking it since being released. The nurse talked to me about making sure not to get behind the pain, but I m concerned that I m taking it while the nerve block is still active - unnecessarily and putting more medicine in my liver. It s 2:30 am here and I m reluctant to call the doctor. 1 Is there risk in taking the oxycodone if I don t need it to manage the pain? 2 If I discontinue taking it and wait until I start feeling pain in my leg, will I have enough time for it to be effective, and will I risk being behind and catching up? 3 Am I keeping the oxycodone in my system for the initial wearing off of the nerve block? 4 Will the nerve block wear off all at once or gradually? Thank you, Susan  <response>: Hi, How bad is Chat Doctor. 5 gallons could be fatal. 1 325 of Tylenol is safe. It takes ten times that at one time to be bad for the liver. So, it is safer than water. In each case, having taken a gallon or a Tylenol yesterday isnt going to make taking it again today unsafe. So, the Tylenol issue wont accumulate. On the other hand, there are a lot of reasons not to overtake narcotics. You can get used to them in a few days and then they dont work as well because youve gotten used to them. It is equally true that if you dont have any pain, you dont know when to take them. The other feature the nurse is correct about is that they start working only about 40 min after you take them. Their peak effect is like at 90 min. So, if you wait on the pain, you will have a lag before relief. But there are also reasons to wait. The nerve block wears off pretty suddenly. Hope I have answered your query. Let me know if I can assist you further. 