The body takes longer to absorb it after a high-fat meal or alcohol. In the rare event you have a painful or prolonged erection lasting 4 or more hours, stop using this drug and get medical help right away, or permanent problems could occur. Stop taking sildenafil and get medical help right away if these effects occur. It is important to take Viagra exactly as prescribed by your doctor or pharmacist. It is important to tell your health care professional about all other medicines that you have taken recently including any kind of supplements and non-prescription drugs. It is important to take Viagra exactly as prescribed by your doctor. Antibiotics, antifungals, and HIV protease inhibitor drugs are all processed in the liver, just like Viagra.Drug Images 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. . Sildenafil (Viagra). This medicine works best when you take it on an empty stomach an hour before sex. The body takes longer to absorb it after a high-fat meal or alcohol. Its effects . Pfizer released Viagra in and, since then, generic versions of the drug have become available, too. Viagra, along with other ED medications such as Cialis (tadalafil) and Levitra (vardenafil), functions as a phosphodiesterase 5 (PDE5) inhibitor.