Fiber supplements usually contain ingredients like psyllium, pectin, polycarbophil or methylcellulose. These are generally safe and tolerated well by the body. However, there are some side effects associated with fiber supplements. These include bloating, gas, stomach cramps. These side effects may reduce as your body adjusts to the fiber supplement. In case they do not reduce, you can discuss it with your doctor. He or she may suggest a different fiber supplement or reduce your current dosage. In rare cases, fiber supplements can cause more serious side effects like rectal bleeding, constipation, bloody stools, dizziness, sweating, rapid pulse, fainting. In such cases, contact a doctor immediately. Remember to drink plenty of water while taking fiber supplements. If enough water is not consumed, these supplements can cause constipation and rectal bleeding. Some studies have shown that fiber supplements interfere with the proper absorption of minerals like calcium, magnesium. People with scleroderma should be careful while using fiber supplements. Although it can enhance well being, promote digestion, it can also cause constipation, bowel obstruction if not taken properly. Therefore, it is best advised to take it under a doctor’s guidance. Allergic reactions to fiber supplements are rare but if you notice symptoms like rashes, itching, swelling, breathing trouble consult a doctor immediately.