Viagra (sildenafil) has been specially designed to treat ED - a condition that can be described as an inability of a male to keep an erection for long enough to have sex. 50 mg is the most commonly recommended dose of Viagra. Depending on your age and health condition, as well as a number of other factors, you may be recommended to take this medicine in smaller doses (25 mg) or larger doses (100 mg). However, this decision should be made by a qualified professional only, which is why it's strongly recommended to see your doctor before you start taking Viagra. Viagra is FDA pregnancy category B, which means that, although this medicine was not originally intended for women, it is unlikely to do any harm to an unborn or nursing baby if taken by pregnant or breastfeeding women. However, since the effects are not studied completely, it's recommended to discuss your pregnancy or breastfeeding with your health care provider before you decide you need Viagra.