Push the plunger of the syringe, then insert the tip into the bottle while holding the bottle upright on a flat surface. If too much is used, the chance of side effects is increased. Place the tip of the syringe into you or your child’s mouth and point it towards the cheek. You’ll soon start receiving the latest Mayo Clinic health information you requested in your inbox. More serious side effects may include a drop in blood pressure or an erection that lasts longer than four hours. · Use sildenafil exactly as directed by your doctor. Do not use more of it and do not use it more often than your doctor ordered. If too much is used, the chance of side effects is increased. A person needs a prescription for medications such as Viagra or Cialis. A primary care physician or a doctor at a telehealth company can provide it. FAQs. What to consider. Cost. Overdose. Ask your doctor. Q&A. Drug Images. What is Viagra? If you have erectile dysfunction (ED), your doctor may recommend that you .