Senna is used in the treatment of constipation and acts by stimulation of intestinal peristalsis or contractions. It is important to recognize that constipation is sometimes caused by factors which should be corrected prior to the regular use of a strong cathartic like senna. Short-term use only is recommended without a doctor's supervision, as cathartics can become habit-forming.

When stimulant laxatives such as senna or Cascara sagrada have been used for a long time, stopping the medication may result in severe constipation. You may need to "retrain" your bowels in order for them to function naturally by gradually lowering the nightly dose of senna. This may take longer than a month to accomplish.

Prolonged use of senna has also been reported to cause chronic diarrhea with excessive electrolyte and nutrient loss, enlargement of the ends of the fingers and toes, and pigmentation of the colon.

Although uncommon, allergic reactions to senna have been reported. Stop taking senna and seek emergency medical attention if you experience symptoms of a serious allergic reaction including difficulty breathing; closing of your throat; swelling of your lips, tongue, or face; or hives.