The best advice is to ask the md who prescribed them to you how often they want you to change them. I have worked with fentanyl patches for over 12 years and I have never changed a patients patch earlier than 72hours unless it had been removed and needed to be replaced. Sometimes the first couple of days you start using them can be difficult because it generally takes a full 24 hours to build up in your system. Take care and be sure to ask your doctor, fenanyl along with all narcotics need to be taken as ordered because they can be dangerous and even cause you to stop breathing if not taken properly.