Generally, taking one capsule of sildenafil lasts 0.5 to 4 hours, although it is impossible to generalize how long it lasts due to individual differences in dosing. Sildenafil is used to treat erectile dysfunction in men and is taken up to once daily, with the recommended daily dose for most patients being one capsule (50 mg). Generally, one capsule of sildenafil is effective for 0.5 to 4 hours. However, due to the severity of each patient’s condition and tolerance to the medication, the duration of effect may vary. Although the effect of sildenafil can be maintained for more than 4 hours, it does not mean that the penis will remain erect during these 4 hours, in the absence of sexual stimulation, sildenafil does not work. During the use of the drug, patients may experience weakness, allergic reactions, abdominal pain and other adverse reactions. This drug should not be used with any form of nitrate and is also contraindicated in people who are allergic to this drug. As a prescription drug, Sildenafil must be used in strict accordance with medical advice.