Drug dosage is gauged by pain relief. There is no standard dose. It may have to be escalated for advanced disease. Equivalent dose tables are available when switching route or changing drugs. Tolerance occurs when increased doses are needed to maintain an effect.
Physical dependence is return of pain when the opiate is cut back.
Neither is addiction. Start with a brief intravenous course of an opioid but the oral course is better. Some patients use self controlled dosage devices. You push a button for an immediate IV dose. Depression, anger, and anxiety can develop and aggravate pain and can be treated.