Take sildenafil exactly as directed. Do not start these medications while taking sildenafil without discussing it with your healthcare provider. Sildenafil comes as a tablet and suspension liquid to take by mouth. Sildenafil works on the PDE5 enzyme in the lungs to relax the blood vessels. Before starting, stopping, or changing any medications while taking sildenafil, please get the advice of your doctor or pharmacist.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. Viagra is approved for this use in males. Sildenafil is used to treat male sexual function problems (impotence or erectile dysfunction-ED). In combination with sexual stimulation, sildenafil works by increasing blood flow to the penis to. How does Viagra work? Viagra is used to treat erectile dysfunction (ED). It decreases ED symptoms by helping you get and keep an erection. Erections happen when a protein called cyclic.