Macitentan is primarily used in the treatment of pulmonary arterial hypertension (PAH), a condition characterized by high blood pressure in the arteries of the lungs. It works by blocking the action of endothelin, a substance that narrows blood vessels, thereby helping to relax and widen these vessels. This improves blood flow and reduces the strain on the heart, alleviating symptoms such as shortness of breath and fatigue. It is often prescribed for long-term management to slow disease progression and improve exercise capacity. Patients typically take it orally once daily, and it is suitable for use in combination with other PAH therapies. Regular monitoring is required to assess its effectiveness and manage potential side effects.