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Fiber for constipation

Goal: What trials of fiber supplements used for chronic constipation, and what share of people responded.

Each protocol describes what studies used, for one goal or for one group of people. It is not advice for you: talk to a doctor before you start a supplement.

Updated 4 Nov 2026
Dose

More than 10 g of fiber a day gave the higher response in a review of 16 trials.[1] The European Medicines Agency (EMA) gives 7 to 11 g of psyllium husk a day for adults and 3 to 8 g for children from 6 to 12 years.[2]

Form

Psyllium and pectin had significant effects.[1]

When to take

In 1 to 3 doses during the day, with at least 30 ml of liquid per 1 g, and not right before bed.[2]

How long

At least 4 weeks for more frequent stools in trials.[1] A single dose of psyllium usually acts in 12 to 24 hours.[2]

What studies found

In 16 trials with 1,251 people, 66% responded to fiber and 41% to control treatment.[1] An earlier review of 7 trials found that 77% of people responded to fiber, against 44% on placebo, with low quality of evidence.[3] Gas was more common with fiber in both reviews.[1][3]

Ask a doctor first

Psyllium can block the throat or gut if taken with too little liquid. It should not be used with stuck stool plus pain, nausea or vomiting unless a doctor advises it.[2] It is not recommended under age 6.[2]

People whose constipation does not improve in 3 to 7 days, and people who take a daily medicine, should ask a doctor or pharmacist.[2][4][5]

References

  1. The Effect of Fiber Supplementation on Chronic Constipation in Adults: An Updated Systematic Review and Meta-Analysis of Randomized Controlled Trials. van der Schoot A, Drysdale C, Whelan K, Dimidi E Am J Clin Nutr, 2022. PMID 35816465
  2. Community herbal monograph on Plantago ovata Forssk., seminis tegumentum. European Medicines Agency, HMPC, 2013. www.ema.europa.eu
  3. Systematic review with meta-analysis: effect of fibre supplementation on chronic idiopathic constipation in adults. Christodoulides S, Dimidi E, Fragkos KC, Farmer AD, Whelan K, Scott SM Aliment Pharmacol Ther, 2016. PMID 27170558
  4. Natural Health Product Monograph: Psyllium, Plantago ovata. Health Canada, 2018. webprod.hc-sc.gc.ca
  5. Psyllium: MedlinePlus Drug Information. MedlinePlus, US National Library of Medicine, 2024. medlineplus.gov