This study compares the effectiveness of two oral medications-melatonin and tranexamic acid -in treating melasma, a common skin condition that causes dark facial patches.

Participants will be randomly assigned to receive either melatonin, tranexamic acid, or a placebo once daily at bedtime for 12 weeks. During this treatment phase, all participants will also apply a broad-spectrum sunscreen and a base cream.

After 12 weeks, participants will stop the oral medication but continue using the sunscreen and base cream for an additional 12 weeks to assess recurrence of melasma.

The study evaluates improvement in skin pigmentation, recurrence after treatment cessation, quality of life, and patient satisfaction.

This clinical trial will be conducted at Benchakitti Park Hospital, Bangkok, Thailand, and will enroll 75 adult participants.

Melasma is a chronic skin disorder characterized by symmetrical, hyperpigmented patches on sun-exposed areas, especially the face. Although its exact cause is not fully understood, hormonal influences, ultraviolet (UV) exposure, and genetic predisposition are contributing factors.

Tranexamic acid (TXA), an antifibrinolytic agent, has shown promising results in treating melasma by inhibiting melanogenesis through the plasminogen-plasmin pathway. Melatonin (MLT), a hormone with antioxidant and anti-inflammatory properties, has also demonstrated potential benefits in melasma management by reducing oxidative stress and interfering with the melanin synthesis pathway.

This prospective, randomized, controlled, evaluator-blinded clinical trial aims to compare the efficacy and recurrence outcomes of oral TXA (500 mg), oral MLT (2 mg), and placebo, each administered once daily for 12 weeks. After discontinuing the oral treatment, all participants will continue using sunscreen and base cream for an additional 12 weeks to evaluate recurrence.

Outcome measures include modified Melasma Area and Severity Index (mMASI), Mexameter-based pigmentation indices, quality of life scores (DLQI), and patient satisfaction (VAS). The study is conducted at Benchakitti Park Hospital and includes 75 adult participants with epidermal or mixed-type melasma.

Inclusion Criteria:

1. Patients with the age above 18 years and above
2. Patients diagnosed with epidermal or mixed-type melasma

Exclusion Criteria:

1. Use of topical medications such as hydroquinone, whitening agents (e.g., arbutin, kojic acid, vitamin C, retinoids, and steroids) on melasma areas within 4 weeks prior to joining the study
2. Chemical peeling within 4 weeks prior to joining the study
3. Use of oral tranexamic acid or any supplements within 3 months prior to joining the study
4. History of laser treatment, dermabrasion, or skin-tightening devices within 6 months prior to joining the study
5. History of botulinum toxin injections, fillers, collagen stimulators, or thread lifts within 12 months prior to joining the study
6. Pregnancy or breastfeeding
7. Use of hormonal contraceptives within 1 year prior to joining the study
8. Personal or family history of thrombotic disorders, such as deep vein thrombosis, pulmonary embolism, stroke, protein C or S deficiency, or antithrombin III deficiency
9. History of more than 2 spontaneous abortion
10. History of impaired kidney function
11. History of cancer
12. Smoking
13. Heart disease (e.g., end-stage heart failure, chronic obstructive pulmonary disease, or use of prosthetic heart valves)
14. History of allergy to oral tranexamic acid or melatonin
15. Patients who are unable to follow up as per the study protocol
16. Patients with Hori's nevus

Individual participant data (IPD) will not be shared due to confidentiality concerns and lack of a formal data-sharing infrastructure. Data will be available upon reasonable request in de-identified, summary form only