n. a drug administered orally for the treatment of erectile dysfunction. By inhibiting the action of the enzyme phosphodiesterase type 5, it elevates local *nitric oxide levels, causing smooth muscle relaxation and increased blood flow to the corpus cavernosum of the penis, which results in erection during sexual stimulation. Sildenafil is also licensed for the treatment of pulmonary hypertension. Side-effects include headache, facial flushing, dyspepsia, nasal congestion, and dizziness. Because of severe adverse reactions, the drug is contraindicated in patients taking nitrate-based drugs, such as *glyceryl trinitrate. Tadalafil and vardenafil are drugs with similar actions and effects.... sildenafil
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