Habitual diarrhea is often referred to as diarrhea on eating, and older, middle-aged, and younger people often seek medical attention for this symptom. Habitual diarrhea is a symptom, but its cause is actually called irritable bowel syndrome. If an elderly person has habitual diarrhea, it is necessary to investigate the cause, whether there is an unclean diet, and if so, to avoid it. The main treatment is to use belladonna plus Saccharomyces boulardii, or belladonna plus pefikon, belladonna plus oxybutynin or oxybutynin plus pefikon, etc. This is the treatment of habitual diarrhea in the elderly. Young people with habitual diarrhea, which is the treatment for the diarrhea type of irritable bowel syndrome, can use Dextran, plus bacterial preparations such as Saccharomyces boulardii or Pefikon, which is very effective. Habitual diarrhea, i.e. irritable bowel syndrome, can be treated with the above methods.