Sildenafil tablets for erectile dysfunction come in different strengths ranging from 25mg to mg. The usual dose is 50mg, when you need it. Do not take it more than once a day. The dose can be increased to mg or decreased to 25mg depending on its effect. Take sildenafil up to 4 hours before you want to have sex.Your doctor may adjust your dose as needed and tolerated. Certain lifestyle choices can help or hinder the effectiveness of Viagra. In this case, just leave out the missed dose and take your next dose at the usual time. Check with your doctor right away if you have a sudden decrease in hearing or loss of hearing, which may be accompanied by dizziness and ringing in the ears. If you often forget doses, it may help to set an alarm to remind you.With Viagra, you’ll take a dose between 30 minutes and 4 hours before you plan to have sex. With Levitra, you’ll take a dose about 1 hour before sexual activity.  · Appropriate studies have not been performed on the relationship of age to the effects of sildenafil in children younger than 1 year of age. Safety and efficacy have not been established. Sildenafil should never be used in children for erectile dysfunction. Viagra basics The active drug in Viagra is sildenafil. It belongs to a group of drugs called phosphodiesterase-5 inhibitors. Viagra comes as tablets you take by mouth. You’ll only need to.In fact, you need to be sexually aroused and stimulated for the drug to take effect. Store mixed oral liquid in the refrigerator. Ask your doctor if you have any questions. Taking antacids as an indigestion remedy can impact the absorption of Viagra. Alternatively, the medicine may be taken 30 minutes to 4 hours before sexual intercourse. Side effects are uncommon and generally mild, if you experience any serious pain or side effects which last longer than hours, seek medical attention immediately.