You can take it in a small dose daily or in a larger dose as needed. It’s available in 25 mg, 50 mg, and mg tablets and lasts up to 18 hours. Alpha-blockers are sometimes prescribed for prostate problems or high blood pressure. Sildenafil Viagra. You can see an in-person provider or speak with a doctor virtually. Vardenafil usually works for 4 to 5 hours.Learn More IF YOU CHOOSE BRAND-NAME VIAGRA, MAKE SURE YOU GET THE BRAND NAME Your prescription may have been filled with a generic version instead of . What is Viagra? Viagra is a brand-name prescription drug that’s approved to treat erectile dysfunction (ED). With ED, you’re unable to have or maintain an erection. . These medicines all work well for ED. When choosing one, tell your doctor or other health care professional what your preferences are, such as cost, ease of use, how .