Chemotherapy regimens not only improve the survival of patients with gastric cancer and colorectal cancer, but also cause obvious adverse reactions of digestive tract, such as chemotherapy-induced oral mucositis, abdominal pain, diarrhea, constipation and so on. These adverse reactions seriously affect the patients' quality of life and the efficacy of chemotherapy. Glutamine is a conditionally essential amino acid in the human body. Previous studies have shown that oral glutamine can help to keep the integrity of mucosal epithelium during chemotherapy and reduce the gastrointestinal side effects caused by chemotherapy. The addition of glutamine to parenteral nutrition can better maintain nitrogen balance and reduce the incidence of infection-related complications. A compound glutamine capsule, composed of L-glutamine and the traditional Chinese herbal formula Si-Jun-Zi-Tang which composed of ginseng, Atractylodes macrocephala, Poria cocos and licorice, has been widely used in China for 23 years to treat many types of gastrointestinal diseases, including gastrointestinal reactions induced by radiotherapy and chemotherapy, ulcerative colitis, irritable bowel syndrome. However, so far, only a small sample of clinical trials have explored the role of glutamine in chemical mucositis, and there is a lack of prospective randomized controlled clinical trials to further verify its value in the prevention and treatment of chemical mucositis. The purpose of this study is to observe the efficacy and safety between a compound glutamine capsule and placebo in the prevention of chemotherapy-induced mucositis in patients with gastric cancer and colorectal cancer in a prospective, randomized, double-blind clinical trial.

Inclusion Criteria:

• Age: 18-75 years old; Sex: Male or female
• Pathologically confirmed gastric adenocarcinoma or colorectal adenocarcinoma.
• Patients are ready to receive chemotherapy regimens containing platinum or irinotecan (targeted therapy could be used at the same time). Patients have not received any anti-cancer treatment before.
• patients are planned to receive the same chemotherapy regimen at least 2 cycles
• A baseline Eastern Cooperative Oncology Group (ECOG) performance status of 0-2.
• Adequate haematopoietic function of bone marrow: neutrophils≥1.5x109 / L, platelets≥75x109 / L; normal liver and kidney function: TBIL≤ 1 upper limit of normal (ULN); ALT and AST ≤2.5 ULN; creatinine≤1.5 ULN.

Exclusion Criteria:

• (Patient-Generated Subjective Global Assessment, PG-SGA)>9 or severe malnutrition (weight loss > 10% or serum albumin < 30 g/L or body mass index < 18.5 kg/m2);
• Patients with severe heart, lung and brain diseases; chronic hepatitis infection, liver cirrhosis, chronic nephritis, kidney dysfunction, etc;
• Patients with infection-related fever;
• Patients who are known to be allergic or intolerant to any of the ingredients used in the study;
• Patients with long-term chronic diarrhea, abdominal pain, constipation or other digestive tract diseases; patients with gastrointestinal symptoms before chemotherapy (≥grade 2 NCI-CTCAE, version 4.0);
• Synchronously receive other treatments that may cause diarrhea, such as radiotherapy;
• Patients who take drugs for microecological regulation of digestive tract such as Combined Bifidobacterium, ChangTai oral liquid, etc;
• Patients take traditional Chinese medicine or antibiotics;
• Unable to understand and sign the informed consent form;
• participants in other clinical trials.