Contraindications of Sildenafil Citrate include: prohibition of concomitant application with nitrate, guanylate cyclase agonists; prohibited for those who are allergic to this drug. The indication for Sildenafil Citrate is erectile dysfunction in men. During the medication period, concomitant use of any form of nitrate and guanylate cyclase agonists (e.g., leucovorin) is prohibited; the drug should be contraindicated in the case of hypersensitivity to the drug. The drug is contraindicated in women, children, people with recent cardiovascular conditions who should not be sexually active. This drug should be used with caution in patients with cardiovascular and cerebrovascular diseases, sickle cell anemia and retinitis pigmentosa. The use of this drug may cause adverse reactions such as headache, flushing, indigestion, nasal congestion, visual abnormalities, diarrhea, vertigo and skin rashes. Care should be taken to start with the lowest dose; abnormal erection after taking the drug should seek medical attention. Patients should seek medical advice to confirm the diagnosis and apply the drug under the supervision of a doctor.