The effects of sildenafil usually last for about 4 hours, but only under conditions that require sexual stimulation. Sildenafil, which treats erectile dysfunction in men, is a short-acting medication that is usually taken about an hour before sexual intercourse and improves blood flow to the penis under conditions of sexual stimulation, thereby increasing the hardness of the erection. The effect of the drug usually lasts for 4 hours, and after sexual intercourse, the drug gradually loses its effect as the libido wanes, and the penis enters a period of weakness. Adverse effects of the drug include facial edema, shock, weakness, pain, rash, tachycardia, palpitations (rapid heartbeat, often accompanied by panic), hypotension, postural hypotension. The drug is contraindicated in women, people who are allergic to the product, children, people whose recent cardiovascular state does not allow them to have sex. Sildenafil is a prescription drug and should be taken under the supervision of a doctor, as well as avoiding coadministration with any nitrate drugs, in order to avoid hypotension, which can jeopardize the safety of life.