Magnotti will be happy to go over your list in a meeting. See also: Generic Viagra Once you settle on a lab, you can begin your research. Prolonged erections can be dangerous. If you have an erection that lasts more than 4 hours, get medical help right away. Resources and support See the Healthy Male site for more information about erectile dysfunction and its treatment.The Savings Offer and Program expire on 12/31/ For further information, call , visit , or write: Viatris Inc., P.O. 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. Key facts. 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. Cialis lasts up to 36 hours in the body, while Viagra lasts 4–6 hours in the body. Both are taken 30 minutes before sex. Cialis can cause limb pain, while Viagra can cause vision change, rash.