Tadalafil is a selective phosphodiesterase‑5 inhibitor used for erectile dysfunction, benign prostatic hyperplasia symptoms, and pulmonary arterial hypertension, working by enhancing nitric oxide cGMP signaling to relax smooth muscle and improve blood flow where PDE5 is expressed. Its prolonged half‑life provides a sustained effect window compared with other agents in the class, supporting both as needed and continuous daily regimens under clinician guidance for sexual activity or urinary symptom control when appropriate. Indications, contraindications, and interaction cautions especially with nitrates and certain cardiovascular conditions are outlined in authoritative drug references and should guide individualized use decisions.