The commonest Negative effects of VIAGRA: headache; flushing; upset tummy; abnormal eyesight, for example changes in color vision (such as having a blue colour tinge) and blurred vision; stuffy or runny nose; back pain; muscle agony; nausea; dizziness; rash.an erection that will not go away (priapism). Should you have an erection that lasts much mo… Read More