Cardiac

• Naproxen can cause pain or tightness in the chest and increase the risk of having a heart attack or stroke, which increases when naproxen is used for a long period of time.
  
  

Digestive

• Digestive side effects of naproxen include upset stomach, nausea, heartburn, vomiting, diarrhea, constipation, bloating and gas.
  
  

Liver

• Naproxen may cause damage to the liver when taken in high doses or for a long time. Symptoms of liver damage include loss of appetite, jaundice, dark urine, light stools, abdominal pain and fever.
  
  

Neurological

• Neurological side effects of naproxen include dizziness, confusion, blurred vision or night blindness, headache and anxiety. According to the Mayo Clinic, people experiencing these symptoms should seek urgent medical care.
  
  

Ulcers

• Taking naproxen in too high of a dose or over a long duration can result in bleeding in the stomach or perforation of the stomach lining, which is a life-threatening condition.
  
  

Sunburn

• Naproxen can increase the body's sensitivity to exposure to the sun and shorten the amount of time it takes to get a sunburn.
  
  

Birth Defects

• According to the Mayo Clinic, if taken during the last three months of pregnancy, naproxen can cause birth defects. Naproxen can also pass into breast milk and should not be taken by nursing mothers.