Background: Myofascial pain syndrome (MPS) is a painful musculoskeletal condition. The prevalence of MPS ranges from 5.9% to 38.7% in the general population. “Thor-ra-nee-san-tha-kat” (TRK) is a traditional formula included in the Thailand National List of Essential Medicines for the treatment for muscle pain caused by abdominal rigidity and for severe constipation.

Objectives: The authors employed a pilot single-blind, randomized-controlled trial to compare the effectiveness of TRK and naproxen for the treatment of chronic upper trapezius MPS.

Materials and Methods: Seventy-six male and female subjects, ages 25–55 years, who met the inclusion criteria were equally randomized into two groups to receive either two 500 mg capsules of TRK once daily before bed or two 250 mg naproxen tablets twice a day after meals for 14 days. Subjects assessed their level of pain using the numerical rating scale. Cervical range of motion (CROM) was determined using a goniometer, and pressure pain threshold (PPT) was assessed using an algometer. Adverse drug reactions were recorded and all items were compared within and between groups, before and after treatment.

Results: The results revealed that patient pain scores after 14 days of treatment were much improved with mean differences exceeding the reference minimum clinically important difference (MCID) in both groups. However, the changes in CROM and PPT values were small and did not surpass their respective reference MCIDs except for the right lateral bending CROM for naproxen treatment. The adverse drug reactions were mild, with watery stools reported by 47% of patients in the TRK-treated group and constipation reported by 24% of those in the naproxen group.

Conclusion: The administration of TRK formula for 14 days was safe and as effective as naproxen at providing short-term relief of pain in patients with chronic upper trapezius pain.