However the dose is usually not more than 40 mg 3 times a day. Sildenafil should not be used with any other medicine or device that causes erections. These can happen for a number of reasons, including certain medical conditions that increase prolactin, steroid abuse by bodybuilders, hypo- or hyperthyroidism too little or too much thyroid hormone , or hormone therapy for cancer treatment. The four main medicines taken by mouth for erectile dysfunction are: Avanafil Stendra. This medication is taken with or without food an hour before sex. Push the plunger of the syringe, then insert the tip into the bottle while holding the bottle upright on a flat surface. Remove the cap by pushing it down and twisting it counter-clockwise.Read and follow these instructions carefully before you start using sildenafil and each time you get a refill of your medicine. Ask your doctor if you have any questions. Adults 65 . Sildenafil (Viagra). Tadalafil (Cialis). Vardenafil. These medicines are called PDE5 inhibitors. They enhance the effects of a chemical the body makes that relaxes muscles . If you are between the ages of 18 and 60, take no other medication or have no other medical conditions, side effects you are more likely to experience include.