Headache, heartburn, diarrhea, flushing, nosebleeds, sleeping disturbances, muscle pain, color vision changes, and sensitivity to light are all potential generic Viagra side effects, though they are for the most part temporary. Conversely, other adverse effects are more severe and may require medical attention, such as vision loss, blurred vision, heating loss, tinnitus, lightheadedness, chest pain, fainting, and allergic reaction symptoms. However, not all users experience side effects, and those who do sometimes just require a generic Viagra dosage adjustment.