Sildenafil belongs to a group of medicines called phosphodiesterase 5 PDE5 inhibitors. Erectile dysfunction is a condition where the penis does not harden and expand when a man is sexually excited, or when he cannot keep an erection. If you prefer, you may contact the U. Key facts It usually takes 30 to 60 minutes for sildenafil to work for erectile dysfunction. Payment options: Consider how you’d like to pay. Box , Mission, KS If your pharmacy does not participate, you may be able to submit a request for a rebate in connection with this Savings Offer.Sildenafil (Viagra) is a medicine used to treat erectile dysfunction (ED, also called impotence). Sildenafil works by helping to relax the blood vessels in the penis, allowing more blood to flow in and cause an erection. You should take sildenafil about an hour before planned sexual activity, so it has time to work. See also: Generic Viagra. Once you settle on a lab, you can begin your research. Some students choose to volunteer in the lab (anywhere from hours per week). Starting in your junior spring you can receive course credit for your lab work by enrolling in Neurobiology What can I use instead of Viagra? As an alternative to Viagra, a person may wish to try any of the following: Alternative oral drugs: Including vardenafil, tadalafil, and avanafil.