What Is the Herb Senna?

How Senna Works

• When experiencing constipation, take senna as a short-term treatment, meaning do not take senna for more than two weeks; otherwise, your body can become dependent on senna to move your bowels. Senna contains a large number of chemicals known as sennosides. These sennosides irritate your bowel lining, creating a laxative reaction. The laxative effect occurs from 8 to 12 hours after taking the senna. Take senna orally, which may cleanse your colon effectively before having a colonoscopy or rectal surgery.

Drug Interactions

• As a stimulant laxative, senna taken with diuretic drugs, which some call water pills, may cause your body to decrease too much potassium. Some examples of diuretic drugs include furosemide or Lasix, chlorthalidone or Thalitone and chlorothiazide known as Diuril. Low potassium levels of senna can also heighten the side-effect risks of the drug digoxin commercially known as Lanoxin, used to treat heart failure. Also, if you take the blood-thinning drug warfarin, known as Coumadin, senna can increase bleeding if you have diarrhea from taking the laxative.

Dosages

• The National Institutes of Health recommends for adult constipation and for children age 12 and up, take 17.2 mg of senna daily. Do not take more than 34.4 mg each day. Children under the age of 12 can take 8.5 mg daily and the elderly can take 17 mg of senna each day. After a pregnancy, take 28 mg for constipation in two divided doses.

Warnings

• If you have abdominal pain, appendicitis, Crohn's disease, prolapse, ulcerative colitis or hemorrhoids, do not use senna. Avoid using senna if you already have loose stools, diarrhea or dehydration -- senna may only worsen these conditions. If you have heart disease, consult your doctor before taking senna, since this laxative can worsen heart disease due to electrolyte disturbances. Your body's cells need electrolytes found in your blood and tissue fluids to regulate the water molecules flowing across your cells. When pregnant or breast-feeding, use senna only for the short term in the recommended dosages. The small amount of senna entering the breast milk does not cause changes in the stools of the baby.