You might need to take Viagra on a few different occasions before it starts to work for you. Related Story Can porn cause erectile dysfunction? See a doctor — if you buy Viagra Connect over the counter, it’s still important that you see your doctor in the next six months so that they can check you over for any underlying causes of your ED. It lasts 4 to 5 hours, or longer if you have mild to moderate ED. Medicines that you take by mouth are called oral medicines. 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. People who have had a heart attack or stroke in the last six months.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 as a treatment for . Viagra is used to treat erectile dysfunction (impotence) in men. Another brand of sildenafil is Revatio, which is used to treat pulmonary arterial hypertension and improve exercise . Sildenafil (Viagra brand) increases blood flow to the penis following sexual stimulation. It does this by blocking the enzyme responsible for the breakdown of cGMP. cGMP is a .