Sildenafil and vardenafil each have their own characteristics and it is impossible to tell which one is more effective. Both sildenafil and vardenafil are medications used to treat erectile dysfunction. Contraindications to the former drug include hypersensitivity to the product, concomitant administration of any dosage form of nitrates, guanylate cyclase agonists (e.g., leucovorin). Common adverse reactions include back pain, myalgia, headache, and nasal congestion. Contraindications to the latter include those who are allergic to the product, those who are taking any form of nitrates, those with previous visual loss due to non-arteritic optic nerve ischemic lesions, those with severe cardiovascular and cerebrovascular dysfunction, those with severe hepatic impairment, those with hypotension, and those with end-stage renal disease requiring dialysis. Common adverse reactions include headache, dizziness, dyspepsia and other symptoms. The above two drugs can not be clearly determined who is more effective, mainly because of individual differences, so that the efficacy of the drug is not the same for each person, so that the two drugs have their own adaptive groups. The specific use of the drug should be guided by a specialized physician.