Before taking sildenafil, tell your doctor and pharmacist if you are allergic to sildenafil, any other medications, or any of the ingredients in sildenafil tablet or suspension. Do not start these medications while taking sildenafil without discussing it with your healthcare provider. 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. Please expect up to 4 to 6 weeks for reimbursement. These medicines are called PDE5 inhibitors.Below are details about Viagra dosages commonly used to treat erectile dysfunction (ED).. Viagra form. Viagra comes as tablets that you swallow. Viagra strengths. Viagra tablets . Sildenafil (Liqrev, Revatio) is used to improve the ability to exercise in adults (Liqrev, Revatio) and children 1 year of age and older (Revatio) with pulmonary arterial . 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.