Methadone in Neuropathic Pain

Inclusion Criteria: * Age greater than18 years * Chronic neuropathic pain of central or peripheral origin for 3 months or longer as determined by the study physician and a score of 4/10 or greater on the DN4 * Moderate to severe pain as defined by average 7-day pain score of greater than 4 on an 11-point numerical rating scale for pain intensity (NRS-PI). * Physician has identified that an opioid is a valid adjunctive treatment for the chronic neuropathic pain. * Concomitant non-opioid analgesic medications must have been stable for 14 days. * Co-interventions such as TENS, acupuncture and massage must have been stable for 14 days prior to the trial * If taking an opioid, maximum dose of opioid in oral morphine equivalents (OME) is 90 mg/24 hours. * Ability to follow the protocol with reference to cognitive and situational conditions; e.g., stable housing, able to attend follow-up visits. * Willing and able to give written informed consent. Exclusion Criteria: * Patients on a dose of opioid that exceeds 90 mg/24 hours in OME * Pregnant or lactating women (women of childbearing potential must have negative pregnancy test) * History of psychosis * History of (within the past 2 years) , or current, substance dependency disorder * Excluded medications are listed in Appendix 1. * Presence of clinically significant cardiac or pulmonary disorder on physical exam that would compromise participants' safety in the trial as judged by the study physician. * Presence of significant conduction delay, ischemia or arrhythmia on screening ECG * Presence of severe pain disorder other than the chronic neuropathic pain under study that would interfere with patient's ability to determine effect of study treatment on the chronic neuropathic pain * Abnormalities above 1.5 times upper range of normal on screening CBC, blood chemistry including BUN, Cr, LDH, AST, ALT * Patients with a history of allergy to any opioid. * Participation in another clinical trial in the 30 days prior to enrolment.