The diarrhea half a month is not good to consider with the irritable bowel syndrome, ulcerative colitis, rectal cancer, etc., can be prescribed the use of montelukast, bifidobacterium bifidum, mesalazine and other drugs or surgical treatment. 1. Irritable bowel syndrome: clear irritable bowel syndrome caused by diarrhea for half a month is not good, can be prescribed with antidiarrheal agent treatment, such as montelukast, loperamide, difenocoumarol and so on. Some patients can also be prescribed with 5-hydroxytryptamine receptor antagonists to reduce the frequency of defecation, such as alosetron; prescribed with bifidobacteria, lactobacillus and other intestinal microecological agents to correct intestinal flora imbalance. 2. Ulcerative colitis: ulcerative colitis patients should avoid the use of antidiarrheal agents, opioids, etc., in order to avoid inducing colonic dilatation. Patients need to treat the primary disease. Usually, patients can follow the doctor’s prescription of aminosalicylic acid preparations, such as lauzasulfapyridine, mesalazine, etc.; when the effect is not good, glucocorticosteroids such as prednisone and methylprednisolone can be used. 3. Rectal cancer: some people who have diarrhea for half a month should be alerted to rectal cancer. Those who are diagnosed with the disease can cooperate with doctors according to their conditions to remove the lesions through surgery, and after surgery, they can also combine with chemotherapy, radiotherapy, targeted therapy and interventional therapy, etc., so as to control the progress of the disease and improve the uncomfortable symptoms caused by rectal cancer. There are many reasons why diarrhea is still not well after half a month, such as Crohn’s disease, chronic pancreatitis and so on. It is recommended to consult doctor as soon as possible for examination, follow the doctor’s instruction after clarifying the cause of the disease, pay attention to the rationality of daily diet, and consult doctor regularly for rechecking.