Sildenafil is a medication used to treat erectile dysfunction, and the effects of a single capsule of sildenafil in men usually last for about four hours. Sildenafil, or sildenafil citrate, is a type 5 phosphodiesterase inhibitor that can be used to treat erectile dysfunction. For most patients, the recommended dose is 50mg, usually taken as needed about 1 hour before sexual activity. When taken, it promotes blood flow to the penile area during sexual stimulation, thereby increasing the hardness of the erection. The effect of one capsule of sildenafil lasts for about 4 hours and gradually loses its effect after completion of sexual intercourse due to loss of libido. This medication is taken up to once a day. The recommended dose of sildenafil does not work in the absence of sexual stimulation. As sildenafil is a prescription drug, a few patients may experience adverse reactions such as facial edema, shock, and fatigue after taking it, patients are advised to strictly follow the doctor’s instructions to use the medication, do not abuse the drug privately, and should also avoid taking it with nitrate drugs to avoid adverse drug reactions.