An inherited eye disease that affects the retina. If you have an erection that lasts more than 4 hours, get medical help right away. These include a heart attack, stroke or a serious heart rhythm disorder in the past six months. Which Is More Effective? Cialis and Viagra are equally effective.Men will no longer require a prescription to obtain the impotence drug Viagra and will instead be able to buy it over the counter at pharmacies. The decision by the UK Medicines and Healthcare. How to Get Generic Viagra An inexpensive blood pressure medication might be an option for some men who suffer from erectile dysfunction By Ginger Skinner Last updated: June . The four main medicines taken by mouth for erectile dysfunction are: Avanafil (Stendra). Sildenafil (Viagra). Tadalafil (Cialis). Vardenafil. These medicines are called PDE5 inhibitors. They enhance the effects of a chemical the body makes that relaxes muscles in the penis, called nitric oxide.