Psyllium: What It Does, How Much to Take, and Safety
Psyllium is a fiber from plantago seed husks. It has the best evidence of any fiber supplement for constipation. Plain powder is the cheapest way to buy it.
Take psyllium with a full glass of water. Do not take it if you have trouble swallowing. Take other medicines 2 hours before or after. All cautions
What psyllium does
- Constipation. US gut doctors’ 2023 guideline found trials for three fiber supplements (psyllium, bran and inulin), and only psyllium “appears to be effective”: about 2 more bowel movements a week than a placebo, from low-certainty evidence (AGA-ACG 2023). UK dietitians strongly recommend it (BDA 2025).
- IBS. US guidelines advise soluble fiber such as psyllium over bran. In trials, about 1 in 7 people improved who would not have on a placebo (ACG 2021; Moayyedi 2014). Ask your doctor first.
- LDL cholesterol. In trials, about 10 g a day lowered LDL slightly, by about 13 mg/dL (see below).
- Blood sugar. If you take diabetes medicine, ask your doctor first. In trials, psyllium lowered blood sugar in people with type 2 diabetes (Gibb 2015).
- Weight. Psyllium is not a weight-loss product. FDA has not found it safe and effective for weight control (21 CFR 310.545).
Why it works: psyllium forms a gel with water. In the gut, the gel holds water in stool and softens it (McRorie and McKeown 2017). McRorie is listed at Procter & Gamble, which makes Metamucil, on a 2015 paper (Gibb 2015, PubMed 26561625).
Psyllium and cholesterol
About 10 g of psyllium a day lowered LDL cholesterol by about 13 mg/dL (0.33 mmol/L) in a review of 28 trials with 1,924 people (Jovanovski 2018). That is a small drop: helpful alongside diet, not a replacement for a statin your doctor prescribes.
FDA also allows a heart-health claim for soluble fiber from psyllium husk, as part of a diet low in saturated fat and cholesterol. What FDA allows, in its words. If you take cholesterol medicine, ask your doctor before adding psyllium.
How much to take
Start with one serving a day and build up to 2 or 3 (Metamucil label). Never take more than your label allows. In trials, more than 10 g of fiber a day, taken for at least 4 weeks, helped constipation; 10 g a day or less did not (BDA 2025; van der Schoot 2022). Konsyl Daily Psyllium Fiber Powder gives 5 g a teaspoon, so that is 3 teaspoons (15 g), the most its label allows. Stir each serving into at least 8 oz of water and drink it right away (21 CFR 201.319). These amounts are for adults. How much psyllium, by product.
Husk, powder, capsules or Metamucil
All are psyllium husk. Powder is the easiest to dose and usually the cheapest per gram. Capsules hold about half a gram each, so they are not a practical way to get 10 g; take no more than the label says. Metamucil adds flavor and sugar or aspartame, and gives 3 g of fiber a scoop. The formats compared, with cost.
Side effects and cautions
- Gas and bloating are the main side effects (AGA-ACG 2023). Building up slowly helps you see what your gut tolerates.
- Choking. Taken with too little liquid, psyllium can swell and block the throat. Do not take it if you have trouble swallowing. Get help at once for chest pain, vomiting, or trouble swallowing or breathing after a dose (21 CFR 201.319).
- Other medicines. Take them 2 or more hours before or after psyllium; laxatives may affect how other drugs work (Metamucil label).
- See a doctor if constipation lasts more than 7 days, or if you have rectal bleeding (Metamucil label).
- Allergy. Psyllium can cause allergic reactions, from breathing the powder or from taking it (Metamucil label). In a study of care-home workers who handled psyllium laxatives every day, 8.6% had a clinical allergy (Bernedo 2008). Stop and get help for hives, swelling or trouble breathing.
- Pregnancy, breast-feeding and children. If you are pregnant or breast-feeding, ask your doctor first. For children, ask your child’s doctor (Metamucil label).
Which psyllium to buy
Our pick, Konsyl Daily Psyllium Fiber Powder, is at the top of the page: the plain psyllium on a public testing list that we could price. The others below cost less per gram, or come flavored or in capsules.
- Buy NOW Whole Psyllium Husks (16 oz) on Amazon
- Buy NOW Psyllium Husk Powder, Organic (12 oz) on Amazon
- Buy Metamucil 4-in-1 Psyllium Powder, Sugar-Free Orange on Amazon
- Buy Member's Mark 100% Psyllium Husk Fiber Capsules on Amazon
| Item | Value |
|---|---|
| NOW whole husk | $0.51 |
| Member's Mark capsules | $0.56 |
| NOW psyllium | $0.75 |
| Konsyl psyllium | $0.87 |
| Metamucil sugar-free | $0.88 |
Our psyllium picks, scored, with cost per 10 g of fiber.
Psyllium guides
How much and how
Which product
Other fiber
Sources
- Chang L, et al. AGA-ACG Clinical Practice Guideline: Pharmacological Management of Chronic Idiopathic Constipation. Gastroenterology. 2023. PubMed 37211380
- Dimidi E, et al. British Dietetic Association guidelines for the dietary management of chronic constipation in adults. J Hum Nutr Diet. 2025. PubMed 41081513
- Lacy BE, et al. ACG Clinical Guideline: Management of Irritable Bowel Syndrome. Am J Gastroenterol. 2021. PubMed 33315591. Moayyedi P, et al. Am J Gastroenterol. 2014. PubMed 25070054
- Jovanovski E, et al. Effect of psyllium (Plantago ovata) fiber on LDL cholesterol and alternative lipid targets, non-HDL cholesterol and apolipoprotein B. Am J Clin Nutr. 2018. PubMed 30239559
- Gibb RD, et al. Am J Clin Nutr. 2015. PubMed 26561625
- McRorie JW Jr, McKeown NM. Understanding the Physics of Functional Fibers in the Gastrointestinal Tract. J Acad Nutr Diet. 2017. PubMed 27863994. McRorie is listed at Procter & Gamble, which makes Metamucil, on a 2015 paper (Gibb 2015, PubMed 26561625).
- Bernedo N, et al. Allergy to laxative compound (Plantago ovata seed) among health care professionals. J Investig Allergol Clin Immunol. 2008. PubMed 18564629
- FDA. 21 CFR 101.81 (soluble fiber and heart disease claim), 21 CFR 201.319 (choking warning) and 21 CFR 310.545 (weight-control ingredients), eCFR, read October 6, 2026. Metamucil drug facts label, DailyMed, read October 6, 2026.
This page is for information. It is not medical advice.