Onpen Gel is a topical analgesic formulation containing Diclofenac diethylamine (1.16% w/w), Linseed Oil (3% w/w), Methyl Salicylate (10% w/w), and Menthol (5% w/w), designed for the relief of musculoskeletal pain and inflammation. Diclofenac diethylamine, a nonsteroidal anti-inflammatory drug (NSAID), inhibits cyclooxygenase enzymes, thereby reducing the synthesis of prostaglandins responsible for pain and inflammation. Linseed Oil, rich in omega-3 fatty acids, contributes to anti-inflammatory effects and supports tissue repair. Methyl Salicylate acts as a counterirritant, producing a warming sensation that helps alleviate deep muscle and joint pain by distracting from the underlying discomfort. Menthol provides a cooling effect, enhancing analgesia through activation of transient receptor potential channels, which modulate pain perception. Onpen Gel is indicated for the symptomatic treatment of conditions such as sprains, strains, arthritis, and other soft tissue injuries. It is applied topically to the affected area, allowing localized action with minimal systemic absorption. Caution is advised in patients with hypersensitivity to salicylates or NSAIDs, and it should not be applied to broken or irritated skin. Onpen Gel offers a multi-mechanistic approach to pain management, combining anti-inflammatory, analgesic, and counterirritant properties for effective symptomatic relief.