This is a Phase III, placebo-controlled, multicenter study with an enriched-enrollment withdrawal (EEW) design to evaluate the efficacy and safety of CAM2038 in opioid-experienced subjects with moderate to severe CLBP that requires continuous, around-the-clock (ATC) opioid treatment ≥ 40 mg morphine equivalent dose (MED). The study includes 5 phases: A Screening Phase (up to 2 weeks), a Transition Phase (up to 2 weeks), an Open-Label Titration Phase (up to 10 weeks), a Double-Blind Treatment Phase including a Final Study Visit (12 weeks), and a Follow-up Phase (4 weeks). The overall duration of participation in the core phase of the study (randomized Double-Blind Phase) is up to 30 weeks, from the Screening Phase through the Follow-up Phase. Subjects who complete the Double-Blind Treatment Study Phase will be offered an opportunity to continue treatment in an open label safety extension for up to 60 weeks. Additional subjects may be recruited to open label safety extension to meet the goal of 100 subjects with 60 weeks of treatment.