Guarana - Side effects

Guarana is also known as Paullinia cupana, paullinia, Brazilian cocoa, guarana bread, guarana paste or gum, and zoom. 
Guarana is also present in some soft drinks imported from South America in a manner similar to American soft-drinks fortified with caffeine.
It helps to lose weight and to stay awake, and can help fitness performances.

Stop taking guarana and seek emergency medical attention if you experience

• a serious allergic reaction including difficulty breathing; closing of the throat; swelling of the lips, tongue, or face; or hives; or
  
• irregular heartbeats or chest pain.
  

Other less serious side effects may also reported with the use of guarana. 
Talk to your doctor or health care provider if you experience

• heartburn;
  
• upset stomach;
  
• loss of appetite;
  
• constipation or diarrhea;
  
• nervousness, irritability, or anxiety;
  
• sleeplessness;
  
• irregular heartbeats;
  
• headache.
  
  (via drugs.com)