Psyllium Fiber

Psyllium Fiber

PEP Topic 
Radiation-Induced Diarrhea

Psyllium is a specific form of soluble fiber. Soluble fiber has been used to treat diarrhea because of its ability to absorb fluid and increase the weight of stools.


Likely to Be Effective

Research Evidence Summaries

Murphy, J., Stacey, D., Crook, J., Thompson, B., & Panetta, D. (2000). Testing control of radiation-induced diarrhea with a psyllium bulking agent: A pilot study. Canadian Oncology Nursing Journal, 10(3), 96–100.

doi: 10.5737/1181912x10396100

Study Purpose:

To study the effectiveness of psyllium fiber (Metamucil®) taken during pelvic radiation treatment for prostate or gynecological cancer

Intervention Characteristics/Basic Study Process:

The experimental group received 1–2 teaspoons psyllium fiber. The control group did not receive any psyllium fiber. Patients in both groups were given a booklet titled “Nutritional Guidelines to Help Control Diarrhea.” Patients kept diaries from day 1 of recruitment through 28 days post-treatment, recording the number of bowel movements per day, consistency of stools, amount of antidiarrhea medication taken, and daily dose of psyllium fiber (for the experimental group).

Sample Characteristics:

  • The study reported on 84 patients (72 males and 12 females).
  • Patients had prostate or gynecologic cancer and were undergoing radiotherapy to the pelvis of at least 4,000 cGy in 20 fractions. 
  • Patients with gastrointestinal (GI) disease, tumors of the GI tract, or regularly using laxatives or antidiarrheal medications were excluded from the study.

Study Design:

This was a nonblinded, randomized controlled trial.

Measurement Instruments/Methods:

  • Diarrhea was assessed using the Murphy Diarrhea Scale, which is a scale that has not yet been validated but is based on preexisting scales.
  • A day with diarrhea was defined as any one of the following.
    • 4–6 bowel movements (BMs) more than normal limits for the patient
    • One or more watery BMs
    • 2-3 loose BMs more than normal limits for the patient
    • Use of antidiarrhea medications
  • Severity rankings were as follows.
    • Mild: Less than 11% of days with diarrhea
    • Moderate: 11%–20% of days with diarrhea
    • Severe: More than 20% of days with diarrhea
  • Researchers identified the mean severity score for diarrhea, incidence of diarrhea, mean time to onset of diarrhea, mean duration of diarrhea (in days), and the mean percentage of days in which patients took antidiarrhea medication.


  • Psyllium fiber was effective in reducing the incidence and severity of radiation-induced diarrhea.
  • A statistically significant difference was found in severity (p = 0.030) and incidence (p = 0.049) of diarrhea.
  • No statistical difference was found in mean time to onset of diarrhea, duration of diarrhea, or percentage of days in which patients took antidiarrhea medications.
  • Psyllium fiber was well-tolerated, and patients had no complaints of GI side effects.
  • The cost of psyllium fiber is low.


Psyllium fiber is a well-tolerated, low-cost, effective intervention for reducing the incidence and severity of radiation-induced diarrhea in patients undergoing pelvic radiation treatment for prostate or gynecologic cancer. 


  • Because this was a pilot study, it was limited in scope.
  • The study had a high attrition rate (60 out of 84 patients completed the study, 30 in each group; patients with inaccurate or incomplete diaries and patients in the non-psyllium fiber group who used psyllium fiber were excluded from final analysis).
  • Proctor and Gamble, manufacturer of Metamucil®, provided partial funding for the study via a research grant.