OPRM1 and Euphoria: The use of opioids (legally and illegally) has risen between10 and 14 times in the last 20 years, with more than 42,000 deathsin 2016 in the USA occurring from opioid overdoses alone.14,15 Most prescribed opioids target the mu-opioid receptor (MOR) in Table 1, which are locatedin the reward areas of the brain.14,16,17 When opioid agonists bind to and activate these receptors,it causes euphoria, which can lead to addiction and severe withdrawalsymptoms after repeated use.