Sildenafil tadalafil vardenafil comparison try not to eat grapefruit or drink grapefruit juice while you are being treated with Sildenafil. Usually, the recommended dose is 50 mg. It is taken approximately 0,5-1 hour before sexual activity. Do not take Viagra more than once a day. A high-fat meal may delay the time of the effect of this drug. Try not to eat grapefruit or drink grapefruit juice while you are being treated with Sildenafil Citrate. Viagra is contraindicated in patients taking another medicine to treat impotence or using a nitrate drug for chest pain or heart problems. This medicine should not be taken by women and children as well as in patients with a known hypersensitivity to any component of the tablet.