Recreational use of opioids, the powerful class of analgesic drugs which includes both illicit and prescription medications, has soared over the past two decades. There are 3 principal classes of opioid receptors, and each drug has specific binding properties and affinities which are responsible for their effects. In addition to their analgesic properties, opioids have a number of side effects, including sedation, itchiness, nausea, constipation, respiratory depression and euphoria, the latter of which is responsible for this class of drug’s recreational appeal, with an estimated 4 million users in the United States each year.