You need a prescription from a doctor to obtain sildenafil. Some medications should not be taken with sildenafil. Push the plunger of the syringe, then insert the tip into the bottle while holding the bottle upright on a flat surface. Follow the directions on your prescription label carefully, and ask your doctor or pharmacist to explain any part you do not understand. For treatment of erectile dysfunction: For oral dosage form tablets : Adults up to 65 years of age—50 milligrams mg as a single dose no more than once a day, 1 hour before sexual intercourse. 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.Is there an over-the-counter version of Viagra? Can I get Viagra online without seeing a doctor? Currently, there are no over the counter alternatives to Viagra available. Yes, you can buy Viagra in the Philippines at Rose Pharmacy in most cities. Mike. 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.