Morphine is the gold standard to which all narcotics are compared. Semi-synthetic derivatives of morphine such as hydromorphone (Dilaudid), oxymorphone (Numorphan, Opana), nicomorphine (Vilan), hydromorphinol and others vary in such ways as duration of action, side effect profile and milligramme potency. Fentanyl has the benefit of less histamine release and thus fewer side effects. It can also be administered via transdermal patch which is convenient for chronic pain management. In addition to the intrathecal patch and injectable fentanyl formulations, the FDA (Food and Drug Administration) has approved various immediate release fentanyl products for breakthrough cancer pain (Actiq/OTFC/Fentora/Onsolis/Subsys/Lazanda/Abstral). Oxycodone is used across the Americas and Europe for relief of serious chronic pain. Its main slow-release formula is known as OxyContin. Short-acting tablets, capsules, syrups and ampules which contain OxyContin are available making it suitable for acute intractable pain or breakthrough pain. Diamorphine, and methadone are used less frequently. Clinical studies have shown that transdermal Buprenorphine is effective at reducing chronic pain. Pethidine, known in North America as meperidine, is not recommended for pain management due to its low potency, short duration of action, and toxicity associated with repeated use. Pentazocine, dextromoramide and dipipanone are also not recommended in new patients except for acute pain where other analgesics are not tolerated or are inappropriate, for pharmacological and misuse-related reasons. In some countries potent synthetics such as piritramide and ketobemidone are used for severe pain. Tapentadol is a newer agent introduced in the last decade.