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. The following information includes only the average doses of this medicine. To use the oral liquid: Shake the bottle well for at least 10 seconds before each use. If too much is used, the chance of side effects is increased. If you prefer, you may contact the U. Your doctor may adjust your dose as needed and tolerated. These medicines all work well for ED.Generic Viagra (sildenafil) is available as a , , , and milligram (mg) pill and in liquid form. It’s meant to be taken as needed — about an hour before sex — but . Viagra dosage is not based on weight, but your age can affect your dosage. Specifically, you may have a lower starting dosage than usual if you’re over age Oral medicines for ED usually work well and cause few side effects. The four main medicines taken by mouth for erectile dysfunction are: Avanafil (Stendra). Sildenafil .