Effectiveness of Opioids in the Treatment of Chronic Non-Cancer Pain

Abstract

For thousands of years, opioids have been used to treat pain, and they continue to be one of the most commonly prescribed medications for pain. It is estimated that 90% of patients presenting to pain centers and receiving treatment in such facilities are on opioids. Opioids can be considered broad-spectrum analgesics that act at multiple points along the pain pathway. Unfortunately, opioids also have the potential for great harm, with multiple side effects and potential complications, some of which are lethal. They are also uniquely addictive, which can lead to misuse and diversion. We reviewed the relevant English literature and did thorough manual searches of the bibliographies of known primary and review articles. We utilized pain relief as the primary outcome measure. Other outcome measures were functional improvement, improvement of psychological status, improvement in work status, and evidence of addiction. Shortterm use and improvement was defined as less than 6 months and long-term relief was defined as 6 months or longer. The 3 systematic reviews evaluating long-term effectiveness of opioids for chronic noncancer pain provided unclear and weak evidence. The results of this review showed that many patients in the included studies were dissatisfied with adverse events or insufficient pain relief from opioids and withdrew from the studies. For patients able to continue on opioids, evidence was weak suggesting that their pain scores were lower than before therapy and that this relief could be maintained long-term (> 6 months). There was also weak evidence that long-term opioid therapy with morphine and transdermal fentanyl not only decreases pain but also improves functioning. Limited evidence was available for the most commonly used opioids, oxycodone and hydrocodone. Evidence for the ability to drive on chronic opioid therapy was moderate without major side effects or complications. It is concluded that, for long-term opioid therapy of 6 months or longer in managing chronic non-cancer pain, with improvement in function and reduction in pain, there is weak evidence for morphine and transdermal fentanyl. However, there is limited or lack of evidence for all other controlled substances, including the most commonly used drugs, oxycodone and hydrocodone. Key words: Opioids, opioid effectiveness, pain relief, functional improvement, adverse effects, codeine, morphine, hydrocodone, hydromorphone, fentanyl, methadone.