The most common side effects of VIAGRA: headache; flushing; upset stomach; abnormal vision, such as changes in color vision such as having a blue color tinge and blurred vision; stuffy or runny nose; back pain; muscle pain; nausea; dizziness; rash. If you don’t have a prescription, the drug itself — not just how you use it — may be a problem. Such patients must not apply any out-of-pocket expenses incurred using this Savings Offer toward any government insurance benefit out-of-pocket spending calculations, such as Medicare Part D true out-of-pocket TrOOP costs You are responsible for reporting use of this Savings Offer to any private insurer, health plan, or other third party who pays for or reimburses any part of the prescription filled using this Savings Offer, as may be required. If you have an erection that lasts more than 4 hours, get medical help right away. In some patients, the use of VIAGRA with alpha-blockers can lead to a drop in blood pressure or to fainting medicines called HIV protease inhibitors, such as ritonavir Norvir , indinavir sulfate Crixivan , saquinavir Fortovase or Invirase , or atazanavir sulfate Reyataz some types of oral antifungal medicines, such as ketoconazole Nizoral and itraconazole Sporanox some types of antibiotics, such as clarithromycin Biaxin , telithromycin Ketek , or erythromycin other medicines that treat high blood pressure other medicines or treatments for ED VIAGRA contains sildenafil, which is the same medicine found in another drug called REVATIO. But if someone takes Viagra with cocaine, they’re at risk for priapism, heart attack or stroke. But the side effects of sildenafil citrate, even with a prescription, can be intense.Using drugs without a prescription is risky. Taking sildenafil citrate without a doctor’s supervision can cause priaprism, stroke and even heart attacks. Is it safe to use Viagra without a prescription? | Nebraska Medicine Omaha, NE. Many online companies claim to sell Viagra without a prescription, but this is illegal. What many of these sites actually sell is counterfeit Viagra. It is worth noting that these kinds of. Ordering Viagra Without a Doctor Visit. While many sites sell drugs online illegally, one company called KwikMed offers consumers the option of buying certain medications—the erectile.