NS-304, known as Selexipag, is primarily used in the treatment of pulmonary arterial hypertension (PAH). It functions as a prostacyclin receptor agonist, helping to dilate blood vessels in the lungs, which reduces the pressure on the heart and improves exercise capacity. This medication is particularly beneficial for patients in WHO Functional Class II-III, aiding in delaying disease progression and enhancing quality of life. It is administered orally, offering a convenient alternative to other prostacyclin therapies that require intravenous or inhaled delivery. Selexipag is often used as part of a combination therapy with other PAH-specific medications to optimize treatment outcomes.