However, the dose is usually not more than 80 mg 3 times a day. Erectile dysfunction care at Mayo Clinic Our caring team of Mayo Clinic experts can help you with your health concerns. Oral medicines for ED usually work well and cause few side effects. Sildenafil Viagra. On 6 May , Pfizer , which manufactures Viagra, told the Associated Press they will begin selling the drug directly to people on its site. Cialis reaches its maximum effectiveness two hours after you take it.What Is Viagra? Viagra (sildenafil) was the first erectile dysfunction pill the FDA approved, back in Like Cialis, it’s a PDE5 inhibitor that increases blood flow to the penis. The difference is that the effects of Viagra don’t last very long (only about four to six hours). Viagra is always taken before an anticipated sexual activity. It’s a prescription drug that’s used in adult males* with ED. With ED, you have trouble getting or keeping an erection. To find out more about how Viagra is used for ED, see the “ . Recognizing uncommon, severe side effects. Minor side effects are common when taking ED medication. Still, there are a few side effects that aren’t as common, and some can even be dangerous.
