Psyllium husk, from the plant Plantago ovata, is the active ingredient of Metamucil, according to Drugs.com. Psyllium husk bulks up in the intestines due to the amount of fiber in it. Each dose of Metamucil powder contains approximately 3.4 grams of psyllium husk, which amounts to 2.4 grams of fiber.
The active ingredient delivers soluble and insoluble fiber to the digestive tract, notes the Metamucil website. Soluble fiber dissolves in liquid, and insoluble fiber does not. The kind of fiber found in Metamucil is called viscous soluble fiber, which makes up 70 to 80 percent of psyllium husk. The rest of the fiber content is insoluble.
Psyllium treats constipation, and the medicine comes in oral doses of capsules, powder, granules, liquids, and wafers, says MedlinePlus. This type of fiber absorbs liquid in the intestines and forms a bulky stool. This waste then passes more easily through the large intestines to be eliminated from the body. Powder and granules must be mixed with water before ingestion, and at least 8 ounces of water should be consumed with the medicine for it to work effectively. Patients should not take psyllium for more than one week unless a doctor instructs them to do so. Psyllium may be prescribed to treat diarrhea or high cholesterol.