Viagra side effects. Viagra may cause some unwanted side effects. Side effects may include: sensitivity to light. muscle aches. heartburn. nose bleeding. flushed skin. .Always talk to your doctor about the risks and benefits of any treatment. You may also wish to talk to students in those labs. If you experience chest pain, dizziness, or nausea during sex, seek immediate medical help. How oral medicines differ Each oral medicine for ED has a slightly different chemical makeup. This medicine usually begins to work for erectile dysfunction within 30 minutes after taking it. This medicine is available only with your doctor’s prescription. The following interactions have been selected on the basis of their potential significance and are not necessarily all-inclusive.Viagra vs Cialis? About 75 to 85 percent of the time both Viagra and Cialis are effective drugs for erectile dysfunction. Take sildenafil at least 30 minutes, but no more than 4 hours, before sexual activity (1 hour before is the most effective). Do not take more than once daily. A high-fat meal may delay how quickly the drug begins to work. Examples of Viagra’s more commonly reported side effects include: heache. flushing (temporary warmth, redness, or deepening of skin color) stuffy nose. indigestion (upset stomach) mild vision. Viagra side effects. Viagra may cause some unwanted side effects. Side effects may include: sensitivity to light. muscle aches. heartburn. nose bleeding. flushed skin. .It works for up to 36 hours. An inherited eye disease that affects the retina. As with sildenafil, a high-fat meal or alcohol keep the body from absorbing it as quickly. Learn more about our editorial standards here. May make this condition worse.