Recent heart or blood vessel problems. Getting medication from them could be dangerous and costly because the medication might be fake, diluted, or out-of-date. These include a heart attack, stroke or a serious heart rhythm disorder in the past six months. A real pharmacy will always need to know your prescription. Online pharmacies also may not fill short-term prescriptions, such as those for antibiotics.Viagra (sildenafil) is a brand-name prescription drug that’s used to treat erectile dysfunction (ED). Learn about side effects, warnings, dosage, and more. Read on to learn where to buy Viagra and sildenafil online — plus, more about how Viagra works, its alternatives, and how it compares with other ED medications. Generic Viagra (sildenafil) is an alternative to the branded Viagra drug that can be used for treating erectile dysfunction (ED). It’s now sold by many manufacturers, including online.