Its effects might last longer if you have mild to moderate ED. People with certain diseases should not use Viagra including: those with heart issues, previous strokes, penile abnormalities, certain cancers, certain eye diseases, or abnormal blood pressures. If you have an erection that lasts more than 4 hours, get medical help right away. Earlier this year, a Canadian died upcountry in just such a case. You can take it in a small dose daily or in a larger dose as needed. Oral medicine for ED also might not be safe or work well if you have: Very low blood pressure, called hypotension, or uncontrolled high blood pressure, called hypertension. This boosts blood flow and helps you get an erection from sexual activity. · Although sildenafil is generally considered safe for most penis owners, taking it without a prescription is not recommended. Doing so could lead to adverse side . Still, if your doctor says it’s okay for you to use and you end up paying out-of-pocket, you can still get the generic for a lot less than Viagra. According to price . ED Treatment and Prescription. Generic Viagra. Sildenafil alternatives. Tadalafil (Generic Cialis) Vardenafil (Generic Levitra, Staxyn) Avanafil (Generic Stendra) Show more. 10 .