As with all medications Herceptin can have unwanted side effects. The most commonly reported side effects with Herceptin injections are pain, weakness, fever, nausea, chills, headache, and cough.

Less frequently, serious side effects have occurred during treatment with Herceptin. These include life-threatening heart problems, lung damage, as well as infusion reactions, and fetal harm or death when given to pregnant women. See Black Box Warning section.

Tell your doctor or nurse if you have any of these signs of an allergic reaction: hives; difficulty breathing; swelling of your face, lips, tongue, or throat.

Let your doctor know if you have any of these serious side effects:

• Chest pain or heavy feeling, pain spreading to the arm or shoulder, nausea, sweating, general ill feeling;
• Fast or pounding heartbeats;
• Feeling short of breath, even with mild exertion;
• Swelling, rapid weight gain;
• Cough or wheezing;
• White patches or sores inside your mouth or on your lips; or
• Fever, chills, body aches, flu symptoms.