Ulcerative colitis (UC) is increasingly common, its exact cause has not been elucidated, and it is a lifelong disease. Mesalazine (5-aminosalicylic acid, or 5-ASA) is the main drug used to treat UC. Most patients with UC in China have mild disease and do not need surgery, and can have a good quality of life with mesalazine control. However, there are some patients who are not seriously ill, but always fail to be cured, why is that? There are some basic concepts that we must understand when treating UC. Let’s take a look at these three tables below. 1, UC has a light, medium and severe Refer to the following table for the Truelove-Witts criteria, in addition to the Mayo score as well as the Montreal classification. At present, the American College of Gastroenterology (ACG), the British and Irish Association of Anorectal Medicine, and ECCO all recommend the use of this standard to diagnose severe colitis. If the bowel movements are ≤3 times per day and there is no blood in the stool, and no active inflammation is seen on colonoscopy, it is considered to be in “remission” (i.e., temporarily “better”). Generally speaking, mild and moderate UC can be treated with mesalazine, while severe UC requires hospitalization for further treatment. 2, UC lesions range in size UC generally from the rectum to start the disease, upward spread, in turn, can violate the sigmoid colon, descending colon, splenic curvature, transverse colon, hepatic curvature, ascending colon, cecum, but also can have “inverted ileitis”. The extent of UC is determined by colonoscopy, which determines the therapeutic options and whether oral or topical therapy is indicated. It is difficult for oral mesalazine to reach the furthest reaches of the GI tract: the sigmoid colon and the rectum. These are precisely the two areas most commonly involved in UC. Therefore, suppositories are available for proctitis and enemas for left-sided colitis, and these localized treatments are often preferred. Although the lesion is in the rectum, combined oral therapy is more effective. In extensive colitis (beyond the splenic flexure), there is no doubt that “oral therapy + local therapy” is required. In general, local treatment is essential. 3, mesalazine has a range of action and dose requirements mesalazine through direct contact with the intestinal mucosa to play a therapeutic role, so there is a range of action, and at the same time there are dose requirements. Different dosage forms have different ranges of action. Different drug dosage forms are released at different sites and exert their local efficacy. Mild and moderate UC may be treatable with mesalazine and severe UC will require hospitalization for further therapeutic measures. Conclusion The treatment of UC may seem simple, but there is a lot going on. Through these three tables, we can find that: the disease is different, the treatment program is different. For example, in the acute phase of treatment, how to maintain remission, whether to use hormones or biologics, the dose of hormones, when to stop, how to determine the efficacy of treatment, and so on. We would like to warn you that if you can’t get well from enteritis, you must find a professional doctor for evaluation as soon as possible, and don’t diagnose and treat yourself, so as not to aggravate the condition, and the long-term inflammation will lead to polyps and stenosis of the colon, and the risk of cancer will also be elevated.