Melcyl Lotion contains Methoxsalen 1% w/v, a photosensitizing agent primarily used in the treatment of skin disorders such as vitiligo and psoriasis. Methoxsalen belongs to the class of furocoumarins and functions by intercalating into DNA and, upon exposure to ultraviolet A (UVA) light, forming cross-links that inhibit DNA synthesis and cell proliferation. This mechanism helps in repigmentation of depigmented skin patches in vitiligo and reduces hyperproliferation in psoriatic lesions. Melcyl Lotion is applied topically to affected areas, followed by controlled UVA exposure, typically under medical supervision to minimize adverse effects. It is essential to adhere to recommended dosing and exposure times to avoid phototoxic reactions, including erythema, blistering, and long-term risks such as photoaging or carcinogenesis. Patients should avoid excessive sunlight and use protective measures on non-treated skin. Melcyl Lotion is contraindicated in individuals with hypersensitivity to Methoxsalen, hepatic impairment, or a history of skin cancer. Common side effects may include local irritation, itching, and increased photosensitivity. Proper patient education regarding application technique, UV exposure, and monitoring is critical to optimize therapeutic outcomes and ensure safety during treatment with Melcyl Lotion.