Side Effects of Herceptin

The most common side effects associated with Herceptin in patients with metastatic stomach cancer are:

  • Low white blood cell counts
  • Diarrhea
  • Fatigue
  • Low red blood cell counts
  • Swelling of the mouth lining
  • Weight loss
  • Upper respiratory tract infections
  • Fever
  • Low platelet counts
  • Swelling of the mucous membranes
  • Swelling of the nose and throat
  • Change in taste

The most common side effects associated with Herceptin in patients with 
breast cancer are:

  • Fever
  • Nausea
  • Vomiting
  • Infusion reactions
  • Diarrhea
  • Infections
  • Increased cough
  • Headache
  • Fatigue
  • Shortness of breath
  • Rash
  • Low white and red blood cell counts
  • Muscle pain

Herceptin may cause serious side effects (see "Drug Precautions"). 

  1. Herceptin treatment can result in heart problems, including those without symptoms (such as reduced heart function) and those with symptoms (such as congestive heart failure).
  2. Some patients have had serious infusion reactions and lung problems; infusion reactions leading to death have been reported.
  3. Herceptin can cause harm to the fetus (unborn baby), in some cases death to the fetus, when taken by a pregnant woman.
  4. Taking Herceptin Can Result in Serious and Potentially Deadly Lung Problems, Including:
  • A severe shortness of breath
  • Fluid in or around the lungs
  • Weakening of the valve between the heart and the lungs
  • Too little oxygen in the body
  • Swelling of the lungs
  • Scarring of the lungs