The goal of this clinical trial is to learn if fluoxetine works to treat refractory constipation . It will also learn about the safety of fluoxetine. The main questions it aims to answer are:

Does fluoxetine increase the number of completely spontaneous bowel movements (CSBMs) per week? What medical problems do participants have when taking fluoxetine? Does fluoxetine improve psychological symptoms such as anxiety and depression in participants with refractory constipation? Researchers will compare fluoxetine to polyethylene glycol (PEG, a commonly used laxative) to see if fluoxetine works to treat refractory constipation.

Participants will:

Take fluoxetine (40 mg/day) or polyethylene glycol (once daily) for 6 months. Visit the clinic at baseline, and at 1 month, 3 months, and 6 months for checkups and tests.

Record their bowel movements and any changes in symptoms, including anxiety, depression, and side effects.

Inclusion Criteria:

1. individuals aged 18 to 70 years;
2. patients meeting the Rome IV diagnostic criteria for chronic constipation, defined by at least two symptoms: straining, lumpy or hard stools (Bristol Stool Scale types 1-2), incomplete evacuation, anorectal obstruction, need for manual maneuvers, or spontaneous bowel movements occurring less than three times per week. These symptoms must have persisted for a minimum of six months, with the diagnostic criteria being met for at least the past three months;
3. refractory constipation, defined as the use of at least three medications (including osmotic agents, laxatives, prokinetics, biofeedback and probiotics, surgery) for more than three months, with unsatisfactory treatment outcomes;
4. patients present indications for fluoxetine, such as comorbid depression;
5. patients who voluntarily provided informed consent prior to enrollment.

Exclusion Criteria:

1. women who are pregnant or lactating;
2. presence of cardiovascular conditions, organ dysfunction, immune disorders, or infections;
3. concurrent gastrointestinal organic conditions such as tuberculosis, polyps, Crohn's disease, tumors, etc.;
4. prior abdominal surgeries;
5. use of psychotropic medications; 6) diagnosis of hypothyroidism or Parkinson's disease.