Viagra is used for the treatment of erectile dysfunction. It is a phosphodiesterase-5 (PDE5) inhibitor. Common side effects of Viagra include facial flushing, headaches, stomach pain, nasal congestion, nausea, diarrhea, and an inability to differentiate between the colors green and blue. Loss of hearing, ringing in the ears and dizziness may occur. Get emergency medical help if you have any of these signs of an allergic reaction: hives; difficulty breathing; swelling of your face, lips, tongue, or throat. During sexual activity, if you become dizzy or nauseated, or have pain, numbness, or tingling in your chest, arms, neck, or jaw, stop and call your doctor right away. You could be having a serious side effect of Viagra.
Source: Side Effects of Viagra (Sildenafil Citrate) Drug Center - RxList
New research shows that 522 patients have died while taking Viagra in the first year the drug was on the market. Since its introduction in March of 1998, more than 12 million prescriptions of the blockbuster treatment for erectile dysfunction (ED) have been written. There are continued concerns that the drug could trigger heart problems in some users; already it is not recommended for patients taking nitrates for this reason.
Source: Viagra Linked to 522 Deaths