Box , Mission, KS If your pharmacy does not participate, you may be able to submit a request for a rebate in connection with this Savings Offer. It continues to work for up to 4 hours, although its action is usually less after 2 hours. Do not press on the plunger of the syringe. Place the tip of the syringe into you or your child’s mouth and point it towards the cheek. The amount of medicine that you take depends on the strength of the medicine. Also, the number of doses you take each day, the time allowed between doses, and the length of time you take the medicine depend on the medical problem for which you are using the medicine. When oral medications might not be safe Check with your health care team before you take any medicine for erectile dysfunction.You shouldn’t take Viagra if you’re younger than 18 years. This is because the safety and effectiveness of Viagra haven’t been studied in people of this age group. Viagra and . Most men aged 18 and over can take sildenafil for erectile dysfunction. Most adults and children aged 1 year and over can take sildenafil for pulmonary hypertension. Who may . There’s no specific age at which erectile dysfunction (ED) starts. But ED is much more likely after the age of Although you can’t change your age, you can take steps to improve .