Viagra can cause dizziness, headache, redness, or upset stomach. Changes in vision may also occur, such as increased sensitivity to light, blurred vision, or problems in distinguishing blue and green colors. If any of these effects persist or worsen, tell your doctor or pharmacist promptly.
To reduce the risk of dizziness and lightheadedness, rise slowly when rising from a sitting or lying position.
Remember that your doctor has prescribed Viagra because you have determined that the benefit to you is greater than the risk of side effects.
Many people using this medication do not have serious side effects.
Sexual activity can put extra strain on your heart, especially if you have heart problems. If you have heart problems and experience any of these serious side effects while having sex, stop and get medical help immediately: severe dizziness, fainting, chest / jaw / left arm pain, nausea.
Rarely, a sudden decrease in vision, including permanent blindness, in one or both eyes (NAION) may occur. If this serious problem occurs, stop taking Sildenafil and get medical help right away. You are slightly more likely to develop NAION if you have heart disease, diabetes, high cholesterol, other eye problems (“crowded disc”), high blood pressure, if you are over 50 years old or if you smoke.
Also, in the rare case of having a painful or prolonged erection of 4 or more hours, stop using Viagra and get medical help right away, or permanent problems may occur.
A very serious allergic reaction to this drug is rare. However, get medical help right away if you notice any symptoms of a serious allergic reaction, including: rash, itching / swelling (especially of the face / tongue / throat), severe dizziness, trouble breathing.
This is not a complete list of possible side effects. If you notice other effects not listed above, contact your doctor or pharmacist.