Common ones include: Flushing of the skin. The four main medicines taken by mouth for erectile dysfunction are: Avanafil Stendra. If you have liver problems, discuss with your doctor how Viagra Sildenafil may affect your medical condition, how your medical condition may affect the dosing and effectiveness of Viagra Sildenafil , and whether any special monitoring is needed. Do not drink grapefruit juice when taking Viagra Sildenafil. The changes from baseline in scoring on the two end point questions frequency of successful penetration during sexual activity and maintenance of erections after penetration were highly statistically significantly in favor of VIAGRA.Viagra for ED. Viagra is FDA-approved to treat erectile dysfunction (ED) in males ages 18 years and older. With ED, you’re not able to get and keep an erection that’s firm enough to have sex. 1 Example Street,Anytown, NY USA contact@test1.ru () 67 · You’ll typically take Viagra about 1 hour before sex. You can take the drug 30 minutes to 4 hours before you anticipate sexual activity. Based on how well you respond to this dosage and any side.