If it is not treated right away, priapism can permanently damage your penis sudden vision loss in one or both eyes. These include a heart attack, stroke or a serious heart rhythm disorder in the past six months. The products discussed in this site may have different product labeling in different countries. This condition may require prompt medical treatment to prevent serious and permanent damage to your penis. Alternatively, the medicine may be taken 30 minutes to 4 hours before sexual intercourse. Different brands may not work the same way. The body takes longer to absorb it after a high-fat meal or alcohol.Sildenafil (Viagra). Tadalafil (Cialis). Vardenafil. These medicines are called PDE5 inhibitors. They enhance the effects of a chemical the body makes that relaxes muscles . Viagra; Descriptions. Sildenafil is used to treat men who have erectile dysfunction (also called sexual impotence). Sildenafil belongs to a group of medicines called . Learn about the dosage of Viagra for erectile dysfunction (ED). You can also find information on the drug’s strengths, how to take it, and more. Health Conditions.