Do not press on the plunger of the syringe. Side Effects Along with its needed effects, a medicine may cause some unwanted effects. Alternatively, the medicine may be taken 30 minutes to 4 hours before sexual intercourse. Take sildenafil as needed before sexual activity. If you are taking sildenafil to treat erectile dysfunction, follow your doctor’s directions and the guidelines in this paragraph. Continue to take sildenafil even if you feel well. Push the plunger of the syringe, then insert the tip into the bottle while holding the bottle upright on a flat surface.The cost for sildenafil oral tablet mg is around $10 for a supply of 2 tablets, depending on the pharmacy you visit. Quoted prices are for cash-paying customers and are not . 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. Sildenafil (Viagra) is used to treat erectile dysfunction (impotence; inability to get or keep an erection) in men. Sildenafil (Liqrev, Revatio) is used to improve the ability to exercise in adults (Liqrev, Revatio) and children 1 year of age and older (Revatio) with pulmonary arterial hypertension (PAH; high blood pressure in the vessels carrying blood to the .