With the intensive research on the pathogenesis of Crohn’s disease, there has been a new shift in clinical treatment options, from the traditional choice of anti-inflammatory drugs to a gradual transition to the use of treatments such as immunosuppressive agents and biologics. The decision on pharmacological treatment of Crohn’s disease is in principle based on the degree of disease progression (e.g., active, remission; mild, moderate, or severe), the extent of lesion involvement, comorbidities (e.g., fistula, abscess, intestinal stricture, obstruction, perforation), and post-surgical medications to prevent recurrence. The objectives are mainly to control clinical symptoms, induce remission, promote endoscopic mucosal healing, recovery of intestinal mucosal anatomical and histological structures and functional recovery, delay surgical treatment, avoid the risk of loss of intestinal function, disability and incapacity, and adhere to long-term pharmacological maintenance therapy to prevent recurrence and the emergence of disability. I. Active phase treatment There are currently clinical upstage and downstage regimens for the treatment of active Crohn’s disease, which aim to rapidly induce clinical symptom remission. The advantages of conventional upstage therapy are low cost, while the disadvantages are poor efficacy, induction of infection, high risk of disease progression, non-reduction of surgical intervention, induction of lymphoma, and delayed biological therapy (e.g., gram-like). However, the advantages of using step-down therapy early in the disease are high efficiency, reduced incidence of disease-related complications, improved mucosal healing rate, reduced risk of surgical intervention or avoidance of risk of intestinal disability, and shorter hospital stay, while the disadvantages are possible induction of infection and high cost. 1. Aminosalicylic acid (5-ASA)/sulfosalicylic acid (SASP): The effectiveness of 5-ASA in the treatment of active Crohn’s disease remains controversial. 4 g/d has been reported to reduce active intestinal inflammation, but the efficacy remains uncertain. The British Gastroenterological Society suggests that its efficacy is limited and that the use of ASAP (4-6 g/d) is only effective in Crohn’s disease patients with mild colonic lesions, but it is no longer recommended by the European Crohn’s and Ulcerative Colitis Organization and the American College of Gastroenterology. Our clinical observations have shown that 5-ASA is effective in some patients with active Crohn’s disease, and randomized controlled trial studies are still needed. 2. Antibiotics: Metronidazole, ciprofloxacin or rifaximin are effective in the remission of active Crohn’s disease, especially in Crohn’s disease secondary to infections (e.g., abscess formation, intra-fistula infection, storage pouchitis) and intestinal bacterial overgrowth, and can induce closure of perianal fistulas. However, long-term use causes gastrointestinal discomfort and other side effects, many patients can not adhere to long-term. 3, glucocorticoids: Can rapidly control active Crohn’s disease remission, common glucocorticoids (such as hydrocortisone, prednisone, methylprednisolone) more effectively than budesonide to induce moderate-to-severe small bowel type or colon type Crohn’s disease symptom remission, but its associated side effects more (such as infection, increased blood lipids, centripetal obesity, osteoporosis). Prednisone is generally administered at a starting dose of 40 mg/d for 2-3 weeks, then reduced by 5 mg/week until discontinued. If prednisone is ineffective or non-responsive, or relapses during treatment, consider escalation of therapy (including immunosuppression, class grams, surgery). 4. Immunosuppressants: For patients with active Crohn’s disease, consider cyclophosphamide (MTX, 15-25 mg/wk, im) if glucocorticoid dependence or ineffectiveness occurs, which can effectively control the disease in patients with active Crohn’s disease and prevent relapse during remission. Attention should be paid to the digestive tract (nausea, vomiting, diarrhea, abdominal pain, dyspepsia, orchitis), side effects such as bone marrow suppression, hepatic impairment, headache, bone pain, and pneumonia, and it is recommended to recheck blood and liver function every 4 weeks. MTX has teratogenic effects and should not be used during pregnancy. Azathioprine (AZA) and 6-mercaptoguanine (6-MP) are not recommended alone to induce remission in patients with active Crohn’s disease because of their slow onset of action, but are often used in combination with glucocorticoids to improve efficacy. In addition, the use of tacrolimus has been reported to be effective in active Crohn’s disease, while cyclosporine is not effective in patients with active Crohn’s disease and is not recommended. 5, biological agents: In recent years, clinical use of class gram therapy can effectively treat active Crohn’s disease, induce remission and promote fistula healing. For fistulas combined with abscess formation, it is important to consider the use of gram-like therapy after complete drainage (confirmed by MRI and in close cooperation with the anorectal surgeon) and with the use of effective antibiotics. Most current scholarship suggests early and effective intervention before irreversible destruction of the intestine occurs, with the greatest benefit generally seen within a 2-year history of treatment with classical grams and better results with combined classical grams + AZA than with AZA alone. In conclusion: (1) For early active Crohn’s disease lesions without risk of disabling intestinal injury (< 2 years of history, no immunosuppressive or analog therapy, no severe intestinal destruction such as stricture, fistula, abscess, perforation, etc.), glucocorticoid therapy can be used, followed by immunosuppressive maintenance therapy after symptomatic remission; or intramuscular MTX therapy; or analog or combined AZA therapy. (2) For early active lesions combined with the risk of disabling bowel injury (<40 years of age, extensive lesion involvement in the small intestine and colon, perianal and/or rectal lesions, deep intestinal ulcers pending surgical resection, stenosis and/or perforation possible), opt for direct treatment with classical grams in combination with AZA, or surgery if treatment fails. (3) For early active lesions, combined with severe high-risk disabling lesions, such as intestinal stenosis, obstruction, perforation, carcinoma, abscess (large, with obvious signs of infection), ineffective medical drugs, fistulae that do not heal for a long time (ineffective drugs), and serious impact on quality of life (poor nutrition, immunosuppression, serious side effects of immunosuppressive drugs), surgical treatment is recommended. Second, the remission period treatment In order to prevent the relapse of the disease in remission, life should quit smoking, while avoiding too much meat high-fat food, and advocate more vitamins and fruits. 1, in recent years, a large number of clinical observations found that 5-ASA drugs for remission maintenance efficacy is not certain, do not advocate the recommended use. 2, antibiotics (such as metronidazole) have a certain effect on the condition of patients in remission, but due to long-term use of gastrointestinal and other side effects, affecting the long-term use. 3, glucocorticoids (including budesonide) are not recommended for maintenance treatment due to the induction of various side effects. 4, for Crohn's disease in remission, most scholars advocate the use of adequate AZA or 6-MP for maintenance treatment, paying attention to the regular detection of bone marrow hematopoietic function, liver and kidney function damage, induced lymphoma, and induced infection and other complications, which can generally last 3-5 years. For patients intolerant to AZA and 6-MP, MTX (15 mg/wk, im) is recommended. Classic has also shown good efficacy for maintenance therapy, and the combination of AZA or 6-MP may improve clinical outcomes and maintain fistula closure and prevent fistula recurrence. Postoperative relapse prevention and treatment 1. Postoperative relapse of Crohn's disease refers to the reoccurrence of intestinal mucosal inflammation after surgical removal of the diseased intestinal canal. The former refers to a series of life conditioning and necessary pharmacological interventions to prevent intestinal mucosal inflammation after surgery, with the aim of avoiding or delaying the recurrence of inflammation; the latter refers to the necessary pharmacological treatment of postoperative clinical symptoms or endoscopic mucosal inflammation recurrence. 2, there is still no standardized postoperative prevention and clinical treatment program, life should immediately quit smoking. 3, for the first surgical treatment, if only intestinal lesions, non-smoking low-risk patients, no treatment is needed after surgery, 6-12 months review colonoscopy, if no inflammatory recurrence is found, annual endoscopy follow-up, no treatment is needed. In high-risk patients with a history of smoking, combined with intestinal perforation, lesions involving the ileum and colon, and resection >10 cm, 5-ASA (2 g/d) is recommended as prophylactic treatment, despite the controversial evidence for recurrence prevention in evidence-based medicine, with repeat colonoscopy after 6-12 months, and if no inflammatory recurrence is detected, annual endoscopy follow-up without treatment; if recurrence of intestinal mucosal inflammation is detected If recurrence of intestinal mucosal inflammation is found, the treatment will be changed to oral adequate AZA or 6-MP long-term maintenance therapy and annual colonoscopy follow-up. 4, for patients treated with surgery again, treatment with AZA or 6-MP, recurrent colonoscopy in 6-12 months, if there is no recurrence, continue maintenance treatment, annual colonoscopy follow-up; if endoscopic recurrence, then use class gram treatment, if still ineffective, surgery is recommended. Clinical studies have found that hormones and probiotics are ineffective in the prevention of postoperative recurrence. Although continuous postoperative use of antibiotics, such as metronidazole or ornidazole, was reported to be effective in preventing postoperative recurrence, long-term use was limited by the emergence of serious gastrointestinal and other side effects. Fourth, the treatment of special cases 1, fistula: clinical observations found that class grams have better efficacy on the closure of fistula, can promote fistula healing, maintain the fistula closed state, and can prevent fistula recurrence. Antibiotics (e.g., metronidazole, ciprofloxacin) are helpful in improving symptoms caused by fistulae, especially perianal fistulae combined with abscess infections, but they do not promote fistulae healing. The long-term use of antibiotics can cause side effects, so they cannot be used for long. In addition, purine drugs have a beneficial effect on fistula healing. The use of tacrolimus has been reported to be effective in healing perianal fistulas, but further controlled clinical studies are needed. If medical treatment is ineffective, surgical treatment is required. 2. Extra-intestinal complications: Arthritis and bone nodal pain can be treated with acetaminophen, SASP, 5-ASA, COX2 inhibitor celecoxib, glucocorticoids, MTX, NSAID, and classical grams. If osteoporosis is present, it can be treated with calcium, VitD, and glucocorticoids. Skin lesions (e.g. erythema nodosum, gangrenous pyoderma, etc.) may be treated with glucocorticoids, AZA or tacrolimus, and if ineffective, treatment may be switched to analogs. In case of episcleral sclerositis, conjunctivitis, iritis, or uveitis, glucocorticoid therapy (topical or intravenous) is recommended and can successfully prevent blindness and corneal perforation, and if ineffective, treatment can be switched to gram-like therapy. Ursodeoxycholic acid is effective in combined primary sclerosing cholangitis and cholecystitis, and can improve liver function impairment and reduce the occurrence of colon cancer. 3.Pregnant women: In active lesions, pregnant women taking drugs have a significant impact on the growth and development of the fetus, and it is advocated to get pregnant after the Crohn’s disease is in remission. Generally, 5-ASA is safe for fetal growth during pregnancy and lactation, while SASP can cause hemolysis in newborns and impaired absorption of folic acid, and should be used with caution. Metronidazole and ciprofloxacin have little effect on fetal development, but tetracycline and sulfonamides should be prohibited. Glucocorticoids are generally safe for pregnant women, but a small percentage can enter the fetus through the placenta or into the breast milk, which may affect fetal development. Immunosuppressants (AZA, 6-MP, CsA) may cause preterm delivery and congenital defects and should be used with caution. Conversely, MTX has teratogenic effects and should be contraindicated. Recent clinical observations in Europe and the United States have found that treatment with classical grams during pregnancy is generally safe, with no significant changes in the incidence of teratogenicity, stillbirth and preterm delivery.