I have a prescription for hydrocodone and see my doctor regularly. Every three months he checks my urine for the drug. I don't take it every day for chronic pain as prescribed. How many hours before my appointment should I take one so it shows up in my urine? I am tried of having this discussion as to why they usually don't find any.

Essentially the doctor wants to see if you really are taking the medicine instead of selling it or giving it away. That is a very popular drug in high demand for people who do not have a prescription. Maybe you should ask your doctor to prescribe a different medication for your chronic pain if you don't need to take it every day. Long term use of this particular drug can cause an addition.