Prescription opioid addiction is a growing public health problem and more pharmacologic treatments are needed because current approved medications have had limited patient acceptance (naltrexone), limited availability (methadone), and concerns about misuse and diversion (methadone and buprenorphine). Tramadol is a currently approved medication used to treat moderate-severe pain, and initial studies demonstrate that it may be useful for treatment of the uncomfortable syndrome of opioid withdrawal without producing euphoric effects. This study will determine whether two different doses of extended release tramadol can treat opioid withdrawal and whether tramadol itself produces withdrawal after it is no longer taken.