Stool color may change after taking capecitabine tablets. The drug is known to cause gastrointestinal bleeding under the adverse reactions section of its insert, so black colored stools may occur due to gastrointestinal bleeding. The drug has a selective targeting effect and it is an oral chemotherapeutic agent against tumor cells. It has no cytotoxicity per se, and it can be activated to cytotoxic 5-fluorouracil in tumor cells through a three-step enzyme chain reaction, thus minimizing the damage of 5-fluorouracil to normal human cells. Clinically the drug is used for adjuvant chemotherapy of colon cancer, colorectal cancer, breast cancer and stomach cancer. There are adverse reactions such as nausea, diarrhea, anorexia, vomiting, gastrointestinal bleeding, fatigue, dizziness, headache, and rash after the administration of this drug. It is contraindicated for those who are allergic to capecitabine or any of its excipients; it is contraindicated for patients with severe renal impairment. Diarrhea can be caused during the use of the drug, for the emergence of severe diarrhea patients should be closely monitored, if the patient begins to appear dehydration, should be immediately replenished with fluids and electrolytes; during the period of taking the drug should not be driving a machine, car, boat, engaged in aerial work, mechanical work and operation of precision instruments. If medication is needed, it should be used under the guidance of a specialist.