Sildenafil and tadalafil are both used to treat erectile dysfunction. They have different adverse effects and it is not possible to directly compare which one has fewer side effects. 1. Common adverse reactions to sildenafil include vasodilation, chest pain, stroke, angina, migraine, atrioventricular block, fainting, palpitations, prolonged erection, premature ejaculation, cystitis, breast enlargement, frequent urination, nocturia, decreased vision, visual abnormalities, tinnitus, cataracts, headache, flushing, nasal congestion, nausea, back pain, rash, allergic reactions, and indigestion. Serious adverse reactions include blindness, loss of hearing, heart failure, shock, myocardial infarction, sudden cardiac death, serious cardiovascular and cerebrovascular events, transient ischemic attack, pulmonary hemorrhage, respiratory distress, and cerebrovascular hemorrhage. 2. Common adverse reactions to Tadalafil include headache, hypotension, chest pain, stroke, palpitations, abnormal penile erection, retinitis pigmentosa, headache, nausea, dyspepsia, myalgia, back pain, respiratory tract infections, nasopharyngitis. Serious adverse reactions include myocardial infarction, serious cardiovascular events, sudden cardiac death, loss of vision, loss of hearing, and Stevens-Johnson syndrome. Both drugs are in the phosphodiesterase type 5 inhibitor class and are contraindicated in people who are allergic to any of the components of the above drugs, patients who are taking any form of nitrates, guanylate cyclase stimulators, women, children and other people. It is recommended that patients who are unwell go to a regular hospital in time and follow the doctor’s instructions for medication.