As Viagra can also make some people feel dizzy or lightheaded, this could be made worse if you drink alcohol. It can be dangerous to take sildenafil if you also take medicines called nitrates often given for chest pain. Medicines that block an enzyme called CYP3A4. You can take Viagra either with or without food, but be aware that if you take it with or after a meal it will take longer to start working. Some men will need to start with a lower dose of 25mg prescribed by a doctor — see below. Your tablet should be swallowed whole with a drink of water. People taking the medicine riociguat, or any form of nitrate medication, eg glyceryl trinitrate or amyl nitrite “poppers”.Here are some questions related to Viagra’s use. Does Viagra work for ED? Yes, Viagra works to treat ED in most people. It increases blood flow to the penis to help you get . Viagra (sildenafil) is a common medication used to stimulate erections in men with erectile dysfunction, also known as ED or impotence. Viagra is also licensed . About sildenafil (Viagra) Sildenafil is a medicine used to treat erection problems (erectile dysfunction). Sildenafil is also sometimes used to treat pulmonary hypertension (high .