The purpose of this study is to evaluate the efficacy and safety of Transdermal Therapeutic System (TTS)-fentanyl patch (transdermal patch containing a drug that is put on the skin so the drug will enter the body through the skin) in severe (very serious, life threatening) chronic (lasting a long time) low back pain in Thai participants.

This is an open label (all people know the identity of the intervention), single arm, prospective (study following participants forward in time) study conducted to assess the efficacy and safety of TTS-fentanyl in Thai participants with chronic low back pain. All participants start treatment with 12.5 micrograms (µg) per hour patch. The patches will be replaced every 3 days. On Day 3, and every 3 days thereafter, the TTS-fentanyl dose increases will be considered based on rescue medication consumption and pain assessment. No increase in TTS-fentanyl dose will be performed within the 72-hour dosing interval. The duration of the treatment will be 30 days. Primary efficacy assessment will be pain control rated by participants. Assessment time points will be at Day 0 (baseline), on Day 15 and Day 30 (trial end). At the end of study, global preference on efficacy, side effects and overall satisfaction will also be rated by investigator and participants. Participants' safety will be monitored throughout the study.

Inclusion Criteria: -Chronic low back pain with moderate to severe pain at least 3 months -Participants needed to be treated with strong opioid and haven't been treated with strong opioid in the past -Participants who still had moderate to severe pain (Visual Analog Scale [VAS] >= 4), which was not adequately controlled by weak opioids such as tramadol or codeine at optimal doses (at least 120 milligram [mg] per day for tramadol or 200 mg per day for codeine) for at least 7 consecutive days

-Participants who failed from other treatments such as operation or lack of efficacy of current treatment -Participant who has signed the informed consent form Exclusion Criteria: -Skin disease that prevent the use of the transdermal system or which could affect the absorption of fentanyl or local tolerability -History or suspicion of alcohol or drug abuse within the past 5 years -History of cardiac, nervous system or respiratory disease which in the investigator's judgment precludes participation in the study because of the potential for respiratory depression -Concomitant use of Non Steroidal Anti-Inflammatory Drugs (NSAIDs), Cyclooxygenase - 2 (COX-2), muscle relaxant, topical analgesic during the previous week (unless on stable drug dose for at least 1 month before study entry) -Pregnancy or breast-feeding female; female participants of childbearing potential without adequate contraception

From signing of informed consent until 30 days after the participant has completed the study