I up-voted you because it's a fair question, but the grand-parent is absolutely right: there are plenty of cases where opioids are marginally effective. The management of chronic pain in particular is problematic because opioid tolerance can develop in as little as two weeks. In addition, some people have paradoxical reactions to opioids, i.e. increased pain (http://www.ncbi.nlm.nih.gov/pubmed/21412369). Finally, the side effects of high-dose opioids are no joke.