Opioids are substances that act on the nervous system in a similar way to opiates such as morphine and codeine. In a medical context the term usually indicates medications that are artificially made rather than extracted from opium.he term opioid was first used in the early 1960s. Its basic meaning is opiate-like (opiates being a set of narcotic drugs derived from opium), and many sources do not define it more explicitly than that.