Methadone is a long-acting synthetic opioid used to treat opioid dependence and chronic pain. It prevents symptoms of opioid withdrawal, reduces opioid cravings, and blocks the euphoric effects of short-acting opioids such as heroin and morphine. Patients who are taking methadone for therapeutic purposes should be monitored for compliance by testing both methadone and its major metabolite EDDP. Urine testing is considered to be more useful than blood testing for methadone as it has a window of detection of 1 to 3 days, compared to blood which has a window of detection for only a few hours.