Its effects often last for 4 to 5 hours. Medication and lifestyle changes are normal treatment options for young and old men alike. Shake the liquid well for 10 seconds before each use to mix the medication evenly. In fact, young men seem to react the best to this medication. Sildenafil usually should not be taken more than once every 24 hours.Your doctor may start you on a lower Viagra dosage than usual if you: are age 65 years and older have liver problems, such as cirrhosis (scarring of the liver) have severe kidney . For example, Viagra, the most popular of these supplements, generally starts to work 30 to 60 minutes after you take it, but Cialis works in 16 to 45 minutes after consumption. No . Viagra (sildenafil) is a prescription drug that’s used to treat erectile dysfunction (ED). The drug comes as a tablet you’ll take by swallowing. It’s usually taken as needed about 1 .