Opioids are a class of drugs derived from poppies or chemicals. These drugs, which induce a feeling of euphoria, include illegal drugs like heroin as well as legally available prescription medications like Percocet and morphine. Dependence on opioids can be physical or psychological. Although it is usually both, this is not always the case. Cancer patients, for instance, often develop physical dependencies on morphine through extended medical use, but they do not have the psychological dependence.