Myofascial Pain Syndrome (MPS) is one of the leading causes of both acute and chronic musculoskeletal pain encountered in clinical practice.¹ The most common presentation is low back pain, followed by pain in the neck and scapular regions.² These symptoms significantly affect quality of life and work performance. A common site involved in neck pain syndrome is the trapezius muscle, which may cause pain in the shoulder, neck, and occipital region. In some patients, neurological symptoms such as goosebumps or dizziness may also occur.³ Pain can occur in individuals of all age groups and may be either acute or chronic. It can arise from injuries or various diseases. Pain may result from different pathologies, including nociceptive pain, neuropathic pain, or a combination of both. Current medical treatment guidelines include both conventional medications and herbal extract-based therapies. In the 2022 National List of Essential Herbal Medicines of Thailand, several herbal formulations are indicated for pain relief. Oral preparations include Khasai Sen, Thorani Sandhakhat, and Ya Phasom Thao Wan Priang, while topical preparations include chili-based formulations, plai preparations, and plai oil. These remedies are indicated for the relief of body aches and muscle pain.⁶ Kratom, or *Mitragyna speciosa* (Korth.) Havil., is a plant belonging to the Rubiaceae family. In southern Thailand, it is commonly known as "Thom." Kratom leaves contain a variety of chemical constituents, including alkaloids, flavonoids, triterpenes, and phenolic compounds. Among these, indole alkaloids represent the major group. The principal active compound is mitragynine, which accounts for approximately two-thirds of the total alkaloid content, or about 66% by weight.⁷ Pharmacologically, orally administered mitragynine affects both the autonomic and central nervous systems. It possesses analgesic properties through binding to opioid receptors. Additionally, it reduces pain signal transmission to the brain via the noradrenergic and serotonergic systems.⁸ The mitragynine pain-relief patch used in this study is a product containing kratom extract formulated to deliver 10 milligrams of mitragynine per patch. It is designed as a topical patch, allowing the active ingredient to be absorbed into the outer layers of the skin without entering the bloodstream.¹¹ The patch consists of sodium alginate, pectin, and agar, which are naturally derived polymers commonly used as pharmaceutical excipients. The hypothesis of this study is that this locally acting "mitragynine pain-relief patch" can reduce pain and inflammation through the TRPV1 receptor mechanism described above.

Neck, shoulder, and upper back pain are among the most common reasons patients attend general practice, orthopedic, and rehabilitation clinics. Patients with chronic myofascial pain syndrome (defined as pain persisting for more than three months) may be treated using various approaches depending on symptom severity, accessibility of services, and individual suitability. These approaches include oral medications, topical agents, local injections, acupuncture, physical therapy, and muscle stretching exercises.

Many patients may have contraindications to oral medications, acupuncture, or regular attendance at physical therapy sessions, which can negatively affect their overall quality of life. Currently, topical medications are commonly prescribed for these patients at Hospital; however, treatment outcomes are often suboptimal. Moreover, most topical preparations produce a warming effect and may easily cause skin irritation, particularly in elderly patients with fragile skin. If the mitragynine pain-relief patch demonstrates effective pain reduction, it may be further developed as an alternative treatment option for these patients.

The objective of this study is to evaluate the efficacy of a mitragynine-containing kratom pain-relief patch in patients with myofascial pain syndrome, compared with a placebo patch (a patch containing only the base formulation without kratom extract), and to determine whether there is a difference in pain-relief response between the two groups and, if so, how that difference manifests.