There is no such thing as what are the two most feared reactions after chemotherapy. Generally, the common reactions are gastrointestinal reaction, bone marrow suppression, cardiotoxic reaction, pulmonary toxic reaction, neurotoxic reaction and so on. 1. Gastrointestinal reaction: this reaction is a common toxic reaction after chemotherapy, patients will experience nausea, vomiting, diarrhea, constipation and other discomforts. 2. Myelosuppression: this reaction is a common adverse reaction of antitumor drugs, mainly manifested as a decrease in white blood cells and platelets, etc. However, it will recover on its own in 1 to 2 weeks after stopping chemotherapy. 3. Cardiotoxic reaction: it is common in acute myocardial toxicity and chronic cardiomyopathy, the former can recover by itself after stopping chemotherapy, but the latter can cause congestive heart failure, myocardial ischemia and other diseases. 4. Pulmonary toxicity: Because chemotherapy may damage the lungs, some patients may develop serious interstitial pneumonia and pulmonary fibrosis. 5. Neurotoxic reaction: because chemotherapy is easy to cause central and peripheral neurotoxicity, so patients may have cognitive dysfunction, urinary incontinence, numbness of limbs and other symptoms. When chemotherapy patients have the above symptoms, they should report to the doctor in time and cooperate with the doctor for further treatment.