This is an open-label (both physician and participant know the name of the study drug), non-randomized, multicenter (when more than one hospital or medical school team work on a medical research study) and long-term efficacy and safety study of JNS013 (combination of tramadol hydrochloride (TRAM) with acetaminophen \[APAP\]) in participants with chronic pain (aching sensation that persists for more than a few months. It may or may not be associated with trauma or disease, and may persist after the initial injury has healed. Its localization, character, and timing are more vague than with acute pain). This study consists of 4 periods; screening period: 1 week, treatment period I: 4 weeks, treatment period II: 48 weeks and follow-up period: 1 week. During Treatment Period I, restrictions on concomitant treatments will be established and the participants will be treated with one or two tablets of JNS013, four times daily for four weeks. During Treatment Period II, the participants will be treated for 48 weeks using the same dosing method and dose level for JNS013 as was used during Treatment Period I, permitting modifications to the concomitant drugs/therapies as during normal medical care. Throughout both Treatment Period I and Treatment Period II, the decision will be made to permit the participants to select to use either one or two tablets of JNS013 per dose according to the extent of the participant's pain and tolerability. The total duration of treatment period will be of 52 weeks. Efficacy will be assessed using change from baseline in Visual Analogue Scale for pain (VAS24) score at the pre-defined time point until Week 52. Participants safety will be monitored throughout the study.
