I asked this same question on a large message board used only by LDN users. The response was that the dosage of LDN is so minute that it does not affect the use of pain medications at all. These people had taken everything from morphine to tylenol without any problem while continuing their LDN. For some people, they said it took more of the pain meds than before, but there were no harmful side effects, and they did work, which is your main worry, I believe!
Another thing that might ease your mind is to call Dr. Bihari's office and ask his assistant. He is very helpful, and won't mind answering your questions at all, whether you use Dr. Bihari to get your LDN or not...You can find their phone number at the website www.lowdosenaltrexone.org
Hope this helps! I had this same dilemna when my 16 year old had a 4 wheeler accident and triggered this worry in my mind. He has been on LDN for 2 1/2 months now, and we have seen wonderful results. BTW, he was unharmed in the accident, just a few scrapes, but it did make me wonder what would happen if he needed pain medication. Have a great day!