Treatment of relatively constant moderate to severe pain is the major indication. Although oral formulations are most commonly used, buccal and suppository forms of some drugs are available. In the acute setting, strong agonists are usually given parenterally. Prolonged analgesia, with some reduction in adverse effects, can be achieved with epidural administration of certain strong agonist drugs (eg, fentanyl and morphine). Fentanyl has also been used by the transdermal route providing analgesia for up to 72 h. For less severe pain and in the chronic setting, moderate agonists are given by the oral route, sometimes in combinations with acetaminophen or NSAIDs.