There's no evidence that daily use of fiber supplements — such as psyllium (Metamucil, Konsyl, others) or methylcellulose (Citrucel) — is harmful.
Fiber has a number of health benefits, including normalizing bowel function and preventing constipation. It's best to get fiber from food, because supplements don't provide the vitamins, minerals and other nutrients that fiber-rich foods do. But fiber supplements can contribute to the recommended daily intake.
Fiber supplements can cause abdominal bloating and gas, at least initially. If you have intestinal problems, such as a history of a bowel blockage or Crohn's disease, talk to your doctor before adding a fiber supplement to your diet. It's also a good idea to ask your doctor or pharmacist whether fiber supplements interact with any medications you take.
Fiber supplements can decrease the absorption of certain medications, such as aspirin, carbamazepine (Carbatrol, Epitol, others) and others. Fiber supplements can also reduce blood sugar levels, which may require an adjustment in your medications or insulin if you have diabetes.
If you plan to take fiber supplements, start with small amounts to minimize problems with gas. Also be sure to drink plenty of fluids every day.