CONTEXT: The opioid epidemic has included use of traditional drugs and recently newer synthetics. It is critically important to recognize and identify these new drugs both clinically and through appropriately designed toxicology testing. There is little available information on a synthetic gaining popularity, U-47700. CASE DETAILS: A 23-year-old female presented after using "U4" by nasal insufflation and injection. She was cyanotic with respiratory depression and responded to naloxone in the field. She was found to have non cardiogenic pulmonary edema and hemoptysis which improved with BiPAP. Urine and serum samples were analyzed using mass spectrometry, confirming 3,4-dichloro-N-[(1R,2R)-2-(dimethylamino)cyclohexyl]-N-methylbenzamide or U-47700. The sample was further analyzed elucidating metabolism specifics. Drug and metabolite concentrations were subsequently measured in both serum and urine. The parent compound of U-47700 was detected at 394 ng/mL and 228 ng/mL in serum and urine, respectively. Metabolites detected in appreciable amounts included the desmethyl (1964 ng/mL in urine), bisdesmethyl (618 ng/mL), desmethyl hydroxy (447 ng/mL), and bisdesmethyl hydroxy forms (247 ng/mL) of U-47700. DISCUSSION: U-47700 is a potent mu-opioid receptor agonist and has recently been used recreationally, contributing to hospitalizations and likely deaths in the community. This is a case report describing an exposure to U-47700 with subsequent laboratory analysis. Based upon this one case, parent U-47700 appear to be an appropriate marker of use in a serum sample. However, demethylated metabolites appear dominant as urinary markers of U-47700 use.