Sildenafil is best taken within 1 hour before sexual activity. Sildenafil citrate is a drug for the treatment of erectile dysfunction (impotence), and its mechanism of action is to stimulate the release of nitric oxide from the corpus cavernosum of the penis, relaxing the smooth muscle in the corpus cavernosum, and filling the blood vessels. It is generally recommended that patients take 1 tablet (50mg) 1 hour before sexual intercourse as needed, but it works for 0.5-4 hours before sexual intercourse. It is important to note that Sildenafil Citrate should not be taken at the same time as nitrate medications, including nitroglycerin, as this can cause a sudden drop in blood pressure to unsafe or even life-threatening levels. In addition, side effects such as tachycardia, abdominal pain, edema, and difficulty breathing may occur after taking Sildenafil Citrate. It is recommended to take Sildenafil Citrate under the supervision of a physician to avoid the medication from damaging your body.