Background: It is known that chronic pain makes it difficult to lose weight, but it is unknown whether obese patients (body mass index ≥30 kg/m²) who experience significant pain relief after interdisciplinary multimodal pain rehabilitation (IMMPR) lose weight.

Objective: This study investigated whether obese patients with chronic pain lost weight after completing IMMPR in specialist pain units. The association of pain relief and weight change over time was also examined.

Methods: Data from obese patients included in the Swedish Quality Registry for Pain Rehabilitation for specialized pain units were used (N=224), including baseline and 12-month follow-up after IMMPR from 2016 to 2018. Patients reported body weight and height, pain aspects (eg, pain intensity), physical activity behaviours, psychological distress, and health-related quality of life (HRQoL). A reduction of at least 5% of initial weight indicates clinically significant weight loss. Patients were classified into three groups based on the pain relief levels after IMMPR: pain relief of clinical significance (30% or more reduction of pain intensity); pain relief without clinical significance (less than 30% reduction of pain intensity); and no pain relief. Linear mixed regression models were used to examine the weight changes among the groups with different pain relief levels.

Results: A significant reduction of pain intensity was found after IMMPR (p < 0.01, effect size Cohen's d = 0.34). A similar proportion of patients in the three groups with different pain relief levels had clinically significant weight loss (20.2%~24.3%, p = 0.47). Significant improvements were reported regarding physical activity behaviour, psychological distress, and HRQoL, but weight change was not associated with changes of pain intensity.

Conclusion: About one-fifth of obese patients achieved significant weight reduction after IMMPR. Obese patients need a tailored pain rehabilitation program incorporating a targeted approach for weight management.