Viagra clinically generally refers to sildenafil, which can be used to treat erectile dysfunction in men, but not to treat severe premature ejaculation, and should be used under medical supervision. Sildenafil is a selective inhibitor of cyclic guanosine monophosphate specific type 5 phosphodiesterase, which can increase the content of cyclic guanosine monophosphate in the corpus cavernosum in the presence of sexual stimulation, relax the smooth muscle to allow blood inflow and promote penile erection. It can be used clinically to treat penile erectile dysfunction, but is generally not used to treat severe premature ejaculation. Premature ejaculation should be treated with urology, and can be treated with medications such as dapoxetine, lidocaine gel, or spray under a doctor’s supervision. Sildenafil is forbidden to be used in combination with nitrate drugs such as isosorbide nitrate and guanylate cyclase agonists such as lioresiguanide, or it may cause hypotension. It should be used with caution in patients with cardiovascular disease due to the potential cardiac risk of sexual activity in patients with cardiovascular disease. Sildenafil use may cause adverse reactions such as headache, flushing, dyspepsia and abnormal vision.