Angina severe chest pain , unstable or Arrhythmia irregular heartbeat, within the last 6 months or Blood vessel problems eg, aortic stenosis, idiopathic subaortic stenosis or Heart attack within the last 6 months or Heart failure or Hypertension high blood pressure or Hypotension low blood pressure or Retinal disorders eye problem or Retinitis pigmentosa an inherited eye disorder or Stroke within the last 6 months —Should not be used in patients with these conditions. The following interactions have been selected on the basis of their potential significance and are not necessarily all-inclusive. Because appointments can be brief and there’s often a lot of ground to cover, it’s a good idea to be well prepared. Adults 65 years of age and older—25 mg as a single dose no more than once a day, 1 hour before sexual intercourse. This medicine comes with a patient information leaflet. Work through relationship issues. To use the oral liquid: Shake the bottle well for at least 10 seconds before each use. · ED medications like sildenafil (Viagra), vardenafil (Levitra), and tadalafil (Cialis) can cause side effects, like flushing and headaches, which can be made worse when combined with alcohol. Some ED treatments don’t involve medications and may be safer for you to use while drinking alcohol. YurolaitsAlbert/iStock via Getty Images. For most ED drugs, you need to wait a while before you can expect them to start working. How long varies with the drug. Viagra and Levitra take about 30 minutes to work, and the effects last for. Sildenafil oral tablet is a prescription medication used to treat erectile dysfunction (ED) and pulmonary arterial hypertension (PAH).