Common side effects include headache, flushing, back or muscle pain, nasal congestion, indigestion, and mild dizziness, which are usually short‑lived. Rare but serious risks include chest pain, sudden vision or hearing loss, or a prolonged erection lasting more than 4 hours (priapism), which needs emergency care. It should be avoided in people taking nitrates, those with severe heart or liver disease, very low blood pressure, or recent stroke or heart attack, and alcohol should be limited to reduce side‑effect risk.
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