OBJECTIVES: To evaluate the efficacy and safety of tapentadol ER in patients with moderate-to-severe chronic low back pain.  Health status was evaluated using SF-36 and EQ-5D questionnaires. METHODS: Patients received controlled, adjustable twice-daily doses of tapentadol ER (100-250mg), oxycodone HCl controlled release (CR; 20-50mg), or placebo over a 12-week maintenance period, preceded by a 3-week titration period.  Patients completed the EQ-5D and SF-36 at baseline and at specified visits.  EQ-5D evaluates mobility, self-care, usual activities, pain/discomfort, and anxiety/depression; SF-36 evaluates physical functioning, role-physical, bodily pain, general health, vitality, social functioning, role-emotional, and mental health dimensions. RESULTS: Of 981 patients randomized, 958 were evaluated for efficacy.  Compared with placebo, improvements from baseline to endpoint in the SF-36 physical component summary score were significantly greater with tapentadol ER (least-squares mean difference vs placebo [95% CI], 2.3[1.02,3.58], P<0.001) and oxycodone CR (2.3[1.02,3.56], P<0.001).  Both active treatment groups were associated with significant improvements over placebo in role-physical (tapentadol ER, 9.9[4.21,15.49]; oxycodone CR, 9.4[3.83,15.05]; both P<0.001) and bodily pain (tapentadol ER, 5.5[2.44,8.55]; oxycodone CR, 6.3[3.23,9.29]; both P<0.001).  Additionally, tapentadol ER was associated with significantly better outcomes versus placebo in physical functioning (4.1[0.85,7.33], P=0.013) and vitality (3.2[0.41,6.01], P=0.025), while oxycodone CR was not significantly different from placebo on these parameters (physical functioning, 2.6[−0.66,5.77], P=0.119; vitality, 0.8[−1.99,3.58], P=0.576).  For both active treatment groups, changes from baseline in general health, social functioning, role-emotional, mental health, and mental health summary score did not differ significantly from placebo (all P>0.285).  Compared with placebo, the EQ-5D health status index at endpoint improved significantly compared with baseline with tapentadol ER (0.05[0.01,0.09], P=0.020) and oxycodone CR (0.05[0.01,0.09], P=0.019).  Incidences of treatment-emergent adverse events were placebo, 59.6%; tapentadol ER, 75.5%; and oxycodone CR, 84.8%. CONCLUSIONS: Tapentadol ER (100-250mg bid) significantly improved physical and overall health status in patients with moderate-to-severe chronic low back pain.