clinicaltrials.gov Identifier: NCT00246896.

Pain and depression are the most prevalent physical and psychological symptom-based disorders, respectively, and co-occur 30–50% of the time. However, their reciprocal relationship and potentially causative effects on one another have been inadequately studied. Longitudinal data analysis involving 500 primary care patients with persistent back, hip or knee pain were enrolled in the Stepped Care for Affective Disorders and Musculoskeletal Pain (SCAMP) study. Half of the participants had comorbid depression and were randomized to a stepped care intervention (n = 123) or treatment as usual (n = 127). Another 250 nondepressed patients with similar pain were followed in a parallel cohort. Outcomes were assessed at baseline, 3, 6, and 12 months. Mixed effects model repeated measures (MMRM) multivariable analyses were conducted to determine if change in pain severity predicted subsequent depression severity, and vice-versa. Change in pain was a strong predictor of subsequent depression severity (t-value = 6.63, p < .0001). Likewise, change in depression severity was an equally strong predictor of subsequent pain severity (t-value = 7.28, p < .0001). Results from the full cohort were similar in the clinical trial subgroup. In summary, pain and depression have strong and similar effects on one another when assessed longitudinally over 12 months.