By stopping this enzyme, the drug allows better blood flow into the penis, meaning better erections. It may be difficult to remain firm despite wanting to have sex. It’s available in 50 mg, mg, and mg tablets. Alpha-blockers are sometimes prescribed for prostate problems or high blood pressure. Stendra avanafil : This is an as-needed medication taken 30 minutes before sex and can last up to six hours.Drug Images What is Viagra? Viagra is a brand-name prescription drug . A sildenafil (generic Viagra) membership starts at $20 monthly for six . Since , Viagra has been available over the counter as Viagra .