These medicines all work well for ED. Generic versions of sildenafil, vardenafil and tadalafil are available. It lasts 4 to 5 hours, or longer if you have mild to moderate ED. Side effects Side effects of oral ED medicines are often mild. Tadalafil Cialis. 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.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-comparison site. Optum Store Sildenafil If you are experiencing the symptoms of erectile dysfunction (ED), you may have considered using Viagra or a similar ED medication as a possible . Drug class: Impotence agents Medically reviewed by Sophia Entringer, PharmD. Last updated on Uses Warnings Before taking Dosage Side effects Interactions .