While the sale remains subject to a consultation with a pharmacist, the other restrictions from the trial have been removed, allowing customers over the age of 18 to purchase an unlimited number of pills. Follow the directions on your prescription label carefully, and ask your doctor or pharmacist to explain any part you do not understand. Tell your doctor if sildenafil is not working well or if you are experiencing side effects. These medicines all work well for ED. It is thought that this reduced sales over the Internet and was safer as males could be referred for medical advice if appropriate. Your doctor will tell you not to take sildenafil if you are taking street drugs containing nitrates. Avanafil Stendra.Viagra (sildenafil) is a prescription drug that’s used to treat erectile dysfunction (ED). The drug comes as a tablet you’ll take by swallowing. It’s usually taken as needed about 1 . Sildenafil is in a class of medications called phosphodiesterase (PDE) inhibitors. Sildenafil treats erectile dysfunction by increasing blood flow to the penis during sexual stimulation. . Sildenafil, sold under the brand name Viagra, among others, is a medication used to treat erectile dysfunction and pulmonary arterial hypertension. [4] [8] It is also sometimes used .