Background Despite treatment advances for inflammatory arthritis, a significant amount of patients fail to achieve remission. Other modifiable factors such as diet, physical activity and environmental exposures may be an important area of focus to help patients achieve disease remission and greater overall health. Functional medicine focuses on these lifestyle factors and may be an important adjunctive therapy. In this study, we examined the impact of functional medicine on patient-reported outcomes in patients with inflammatory arthritis. Materials and methods In this 12-week, retrospective study, patients with confirmed diagnoses of rheumatoid arthritis (RA) or psoriatic arthritis (PsA) were treated according to guidelines from the American College of Rheumatology for RA or PSA respectively. Those in the functional medicine group underwent a functional medicine program adjunctive to the standard of care. Patient reported outcomes, such as PROMIS (Patient Reported Outcomes Measurement Information System) global physical health, mental health and pain scores were collected at baseline and 12 weeks. Multivariable statistical modeling was used to identify the impact of functional medicine on patient-reported outcomes. Results 318 patients were screened and 54 patients (mean age 52.9±11.3 years, females 74 (67.9%)), were included. Baseline characteristics were similar in both patient groups with the exception of PROMIS global physical health and pain (PROMIS global physical health score 43 2 ± 6 6 and 39 7 ± 8 7 and pain scores of 3 5 ± 1 9 and 5 2 ± 2 7 in the functional medicine group vs. standard of care group respectively). Using multivariable model to account for these differences, patients in the functional medicine group had a statistically significant reduction in pain (0.92, p-value = 0.007) and change in PROMIS physical health score (2 84, p-value = 0.001) as compared to the standard of care. Changes in PROMIS global mental health scores were also significant and were dependent on age and were greatest in those older than 55. Limitations Retrospective design, baseline difference in patient reported outcomes. Conclusions Functional medicine may have an important role as adjunctive therapy to improve patients' pain, physical and mental health in those who do not see improvement with conventional therapy alone.