The purpose of this trial is to evaluate the safety and efficacy of once daily orally administered GRT6005 in a total of 3 fixed doses compared to placebo in subjects with moderate to severe chronic Low Back Pain (LBP). The study includes a maximum of 21 days screening period followed by a 2-week titration period and 12-week maintenance double-blind treatment period and a 10-14 day safety follow up period. Patients who are eligible for the double-blind treatment period will be randomized to one of the following treatment groups: GRT6005 low-dose, GRT6005 medium dose, GRT6005 high-dose, Tapentadol or placebo.

Inclusion Criteria:

• Chronic Low Back Pain of non-malignant origin and present for at least 3 months.
• Signed informed consent.
• Pain intensity score of 5 or greater on the 11-point numeric rating scale (where 0 indicates "no pain" and 10 indicates "as bad as you can imagine").
• On stable analgesic medications (non-opioid and/or opioid medications) for chronic low back pain with regular intake for at least 3 months and dissatisfied with current analgesic treatment.

Exclusion Criteria:

• Female subjects who are pregnant or are breastfeeding.
• Presence of risk factors for Torsade de Pointes.
• Any clinically significant disease or laboratory findings that may affect efficacy or safety assessments or may compromise the safety during trial participation, e.g., significant unstable cardiac, vascular, pulmonary, gastrointestinal, endocrine, metabolic, neurological, or psychiatric disorders.
• History of acute hepatitis within the past 3 months or chronic hepatitis or a positive result on anti-hepatitis A antibody, hepatitis B surface antigen, or anti-hepatitis C antibody. History of human immunodeficiency virus (HIV) infection.
• History of seizure disorder.
• Chronic low back pain potentially associated with a specific spinal cause.
• Surgery or painful procedure during or within 3 months of enrollment.
• Conditions that contribute and confound the assessment of pain.
• Subjects with impaired renal function.
• Subjects with impaired hepatic functionality.
• Neuromodulation.
• Cancer.
• Clinically relevant history of hypersensitivity, allergy or contraindications to any of the Investigational Medicinal Products' excipients, paracetamol/acetaminophen, tapentadol Hydrochloride, or opioid analgesics (or excipients).