The most common side effect of Viagra and similar drug use is headache, affecting about 16% of users. A drop in blood pressure, transient dizziness, and facial flushing (red face) are reported in 10%. Indigestion occurs in 7% and nasal congestion in 4%. Between 3% and 11% of users report some visual problems while on Viagra. This visual disturbance is described as either blurred vision, increased light sensitivity, persistence of a bluish tinge, or temporary loss of the ability to distinguish between blue and green.Cautions: Viagra, Levitra, and Cialis are absolutely not to be taken by men with heart conditions who are taking nitrates such as nitroglycerine or isosorbide (Isordil, Ismo, Imdur). Certain street drugs such as "poppers" also can cause serious problems if taken with Viagra, Levitra, or Cialis. Ecstasy is a street drug that may increase sexual desire but interferes with performance. This has prompted some men to combine ecstasy with Viagra, Levitra, or Cialis. This mixture (a combination sometimes called "sextasy") can improve erection ability but also causes severe headache and priapism. (Priapism is an abnormally prolonged erection that becomes extremely painful and may result in permanent damage to the erection mechanism.) There are also potentially dangerous effects to your heart from mixing Viagra and similar medications with various other street drugs.