 Methadone and its major metabolite, 2-ethylidene-1,5-dimethyl-3,3-diphenylpyrrolidine (EDDP), are often measured in urine as part of a drug abuse testing program, in plasma or serum to confirm a diagnosis of poisoning in hospitalized victims, or in whole blood to assist in a forensic investigation of a traffic or other criminal violation or a case of sudden death.Methadone usage history is considered in interpreting the results as a chronic user can develop tolerance to doses that would incapacitate an opioid-naive individual.Chronic users often have high methadone and EDDP baseline values.