Microscopic colitis is a form of chronic and recurrent inflammatory bowel disease characterized by non-bloody, watery diarrhea, macroscopically normal colonic mucosa, and characteristic histopathological findings. Some drugs have been described as triggers of colonic inflammation in predisposed individuals, while others may exacerbate microscopic colitis that evolves on its own. We present the case of a patient diagnosed with active microscopic colitis in relation to taking fluoxetine at high doses.