WHAT ARE BULK-PRODUCING LAXATIVES AND HOW DO THEY WORK?
Bulk-producing laxatives or fiber supplements are a class of laxatives used for treating constipation. They work similarly to fiber and increase stool weight and consistency. They also work by absorbing water to make the stool soft and easier to pass. The bulk formed stimulates the intestinal muscles to contract naturally, causing the feces to move along.
HOW ARE BULK-PRODUCING LAXATIVES USED?
As bulk-producing laxatives soften the stool, they are mainly used to treat:
- Constipation
- Irritable bowel disease
- Diverticular disease
- Hemorrhoids
WHAT ARE SIDE EFFECTS OF BULK-PRODUCING LAXATIVES?
Bulk-producing laxatives, when taken orally, can cause these side effects:
- Flatulence
- Fecal impaction (large, hard mass of stools that gets stuck in the colon or rectum)
- Frequent bowel movements
- Stomach cramps
- Abdominal fullness
- Bloating
The information contained herein is not intended to cover all possible side effects, precautions, warnings, drug interactions, allergic reactions, or adverse effects. Check with your doctor or pharmacist to make sure these drugs do not cause any harm when you take them along with other medicines. Never stop taking your medication and never change your dose or frequency without consulting your doctor.
From 
https://www.medicinenet.com/bulk-producing_laxatives-oral/article.htm