Herceptin is trastuzumab for injection, if you have diarrhea after using trastuzumab for injection, you can stop using this product or take antidiarrheal drugs to relieve the symptoms as prescribed by your doctor. Trastuzumab for injection, the main component of which is trastuzumab, is a recombinant DNA-derived monoclonal antibody, which is mainly used in the treatment of early breast cancer, HER2-positive metastatic breast cancer and metastatic gastric cancer. Adverse reactions such as nausea and vomiting, diarrhea, cough, hair loss, fatigue, anemia, and fever can occur during use. The incidence of gastrointestinal reactions such as diarrhea, nausea, and vomiting has been reported in studies to be >20%. If diarrhea symptoms can be tolerated can be left untreated under medical supervision or use antidiarrheal agents such as montelukast to relieve symptoms. If the diarrhea is severe and difficult to tolerate, the dosage can be reduced or switched to other drugs as prescribed by the doctor. Trastuzumab for Injection is contraindicated in people who are allergic to the product and in children. During the process of medication, it is also necessary to monitor the patient’s heart rate, blood pressure, body temperature, cardiac function, blood routine, liver function, etc., so the medication should be carried out under the guidance of health care personnel to avoid adverse effects.