saudigastro.com/patients/fibre-supplements-psyllium
This article is educational and does not replace your doctor's advice. Seek urgent care for any red-flag symptoms.
Drug class
Dietary supplement / bulk-forming laxative (fibre)
Examples
Psyllium husk (ispaghula) powder, capsules or wafers; methylcellulose; calcium polycarbophil; inulin; partially hydrolysed guar gum. Brand names are only examples of product types.
How it works
Our article on dietary fibre covers fibre from food; this page is about concentrated fibre products. Soluble, gel-forming fibres such as psyllium and polycarbophil absorb water, soften the stool and make it bulkier and easier to pass; methylcellulose does a similar job and is barely fermented by gut bacteria, so it causes less gas. Fermentable fibres such as inulin and partially hydrolysed guar gum (PHGG) are broken down by colon bacteria, which can produce gas. Evidence in brief: for chronic constipation, the ACG 2023 guideline recommends psyllium (strong recommendation, based on randomised trials). For IBS, the ACG 2021 guideline suggests soluble fibre (psyllium) for overall symptoms and advises against insoluble fibre such as wheat bran, which can worsen bloating; evidence for PHGG in IBS is limited (small trials). Psyllium modestly lowers LDL cholesterol in meta-analyses, as an addition to, not a replacement for, a healthy diet and any prescribed treatment. For haemorrhoids, a Cochrane review found that fibre reduces persistent symptoms and bleeding. Inulin is a prebiotic with limited evidence of clinical benefit.
What it treats
- Chronic constipation (GOOD evidence for psyllium)
- IBS, especially constipation or mixed type (MODERATE-to-limited evidence for soluble fibre; avoid wheat bran)
- Haemorrhoid symptoms and bleeding, by keeping stool soft (GOOD evidence for fibre as a first step)
- Mild loose stools in some people, because gel-forming fibre can firm the stool (limited evidence)
- A modest lowering of LDL cholesterol with psyllium (MODERATE evidence), as an add-on to diet
How to take it
Start low, go slow: begin with a small amount, increase gradually over a couple of weeks, and follow the label and your doctor’s or pharmacist’s advice on the amount. Powders must be mixed with a full glass of water or another drink, drunk right away (psyllium thickens quickly), and followed by more fluid through the day; without enough fluid fibre can make constipation worse or cause a blockage. Never swallow dry powder, and take capsules with a full glass of water. Effects take several days to appear. Space fibre from other medicines: fibre can reduce the absorption of some of them, so take other tablets about 2 hours before or after, or as your pharmacist advises. Do not use if you have difficulty swallowing, a narrowed oesophagus, a known bowel obstruction or severe constipation with faecal impaction, or unexplained abdominal pain, without seeing a doctor. Choking risk: swelling of the dry product in the throat or oesophagus can cause obstruction, so swallow promptly and do not take it just before lying down.
Common side effects
- Gas, bloating and a feeling of fullness, especially at the start or with fermentable fibres like inulin
- Abdominal cramps or loose stools if the amount is raised too fast
- Constipation getting worse if you drink too little fluid
- Unpleasant texture or taste (many people prefer capsules or wafers)
Serious side effects — call your doctor
Difficulty swallowing, a feeling of food or powder stuck in the throat or chest, chest pain, or drooling after taking fibre
Could be the product swelling and blocking the throat or oesophagus. If you cannot breathe or swallow your saliva, call emergency services now; otherwise go to the emergency department.
Severe belly pain, swelling of the belly, repeated vomiting, or no stool or gas passing
May suggest a bowel obstruction. Stop the fibre and go to the emergency department.
Wheeze, rash, swelling of the lips or face, or trouble breathing (psyllium allergy, more likely after repeated powder inhalation)
Could be a serious allergic reaction. Call emergency services now.
Blood in the stool, black stools, unexplained weight loss, a new change in bowel habit lasting weeks, or anaemia
These are alarm symptoms. Do not treat them with fibre alone; see your doctor promptly for assessment (urgently if bleeding is heavy).
Interactions
Fibre can bind or slow the absorption of other medicines, so space them out (commonly about 2 hours) and ask your pharmacist. Medicines reported to be affected include lithium, carbamazepine, digoxin, thyroid hormone tablets, and mineral supplements such as iron and calcium. Fibre can lower blood sugar after meals, so people on insulin or diabetes tablets may need closer monitoring when they start. Do not combine with other laxatives without advice. Inulin and guar gum can worsen symptoms in people following a low-FODMAP diet for IBS.
Monitoring
Keep a simple stool and symptom diary. If constipation does not improve within 2 to 4 weeks, or if you have alarm symptoms, see your doctor rather than increasing the dose. People on lithium, digoxin, thyroid tablets or diabetes medicines may need their levels or sugar checked, as advised.
When and how to stop
Stop and seek care if you have trouble swallowing, severe belly pain or vomiting, or an allergic reaction. If there is no benefit after a fair trial, stop and ask your doctor about other options. Long-term use of bulk fibre is generally safe when taken with enough fluid.
Pregnancy & breastfeeding
Bulk-forming fibre such as psyllium is generally regarded as a first-choice option for constipation in pregnancy and breastfeeding because it is not absorbed, but take it with plenty of fluid and confirm with your doctor or pharmacist.
In the Saudi context
In Ramadan, taking fibre with a full glass of water at iftar and again before suhoor, and drinking fluids between the two meals, helps avoid constipation; do not take dry powder with little water. Psyllium is sold in pharmacies and herbal shops (attar), sometimes mixed with other herbs or laxatives such as senna; choose a single-ingredient product with a clear label and ask the pharmacist before combining.
Questions to ask your doctor
Save this list or print it before your appointment — doctors appreciate prepared patients.
- Which type of fibre suits my problem (constipation, IBS, haemorrhoids, cholesterol)?
- How should I start, and how do I time it around my other medicines?
- Is it safe for me if I have trouble swallowing or a narrowed bowel?
- How long should I try before we look for other causes?
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Status: Approved for publication by SGA; individual clinician review is ongoing · Published 24/04/2026
For general education only; it does not replace your doctor’s advice. Individual clinician review of this guide is ongoing. SGA clinician? Review this guide