The good news is that you can take steps to improve your relationship with sex and reduce some of the pressure to perform. That means they can increase the amount of Viagra in your body, which can cause unwanted side effects. Sudden vision loss in one or both eyes can be a sign of a serious eye problem called non-arteritic anterior ischemic optic neuropathy NAION. Rogue pharmacies are not licensed to sell in the United States and put you at risk of counterfeit or tainted drugs How Many Online Pharmacies Are There? Anticonvulsants like phenytoin or carbamazepine and an antibiotic called rifampin can all cause Viagra to not do its job. Rarely reported side effects include: an erection that will not go away priapism. Read more on male sexual health on the Sexual Health Australia site.You need a prescription from a doctor to obtain sildenafil. You can buy it from a store-based pharmacy or reputable online pharmacy with a prescription. Some people buy sildenafil online without a prescription. This isn’t a good idea, as you can’t be sure whether these pills contain the medicine or are counterfeit. Viagra, or sildenafil, was the first oral pill approved by the FDA to treat erectile dysfunction. Pfizer released Viagra in and, since then, generic versions of the drug have become available, too. Viagra, along with other ED medications such as Cialis (tadalafil) and Levitra (vardenafil), functions as a phosphodiesterase 5 (PDE5) inhibitor. AdGet a Prescription for ED treatment, discreetly deliverED to your ive Offers · How It Works · Get More Info4/5 ( reviews)Types: Finasteride · Shipping Policy · Tadalafil · Sildenafil.