Sildenafil Citrate, the active ingredient in Cenforce 200 mg and Black Viagra, is a prescription medication that can help to cure erectile dysfunction. It works by relaxing the smooth muscles of the penile area and blood vessel walls. In turn, it prevents the PDE5 enzyme from functioning. This prevents blood from exiting the penis and prolongs the duration of an erection. Moreover, this drug also helps a man stay erect for up to three to four hours.