Constipation in pregnancy is common enough that UK pharmacies see it every day. Rising progesterone slows gut transit, the growing uterus compresses the rectum, and iron supplements — almost universally prescribed for women who test anaemic in the second trimester — add a further constipating push.
The counter options are narrow but effective if used in the right order. This is the approach a UK community pharmacy typically takes in 2026, drawing on NICE CKS and the NHS pregnancy pages.
First: lifestyle measures are not a cop-out
NICE CKS is explicit that dietary fibre, fluid and gentle physical activity are the starting point. That is not because they are cheaper than laxatives — it is because bulk-forming laxatives work poorly without enough fluid, and adequate hydration alone resolves a significant proportion of pregnancy constipation.
A pragmatic script at the counter: aim for 30g of fibre and at least eight glasses of fluid daily, and keep walking if comfortable. The pharmacy can suggest bran, wholegrain cereals, pulses and fruit. This also sets the context for any laxative that follows.
Ispaghula husk and other bulk-formers
Bulk-forming laxatives — ispaghula husk (Fybogel), sterculia (Normacol) and methylcellulose (Celevac) — are generally the first line in pregnancy. They are not absorbed, act locally by drawing water into the stool, and have a long history of safe use across pregnancy.
Two counter-level caveats:
- They need to be taken with a full glass of water and separate from other medications by at least an hour.
- They work in 12–72 hours, not overnight. Women looking for immediate relief will need something else.
Lactulose: the usual second line
If a bulk-former alone is not enough, lactulose is the most commonly recommended osmotic laxative in pregnancy. It is a non-absorbed synthetic disaccharide — the gut does not take it up systemically. NICE CKS and the BNF both consider it suitable for use across pregnancy.
The counter considerations are tolerability rather than safety: bloating and flatulence are common in the first week, and the taste is divisive. Macrogol preparations (e.g. Movicol) are an alternative osmotic with comparable safety in pregnancy and are often better tolerated.
Onset is 24–48 hours.
Stimulants: reserved, not first
Senna and bisacodyl are stimulant laxatives. NICE CKS advises they can be used short term in pregnancy if bulk-formers and osmotics are insufficient, but they are not a first-line choice. The historical concern about senna inducing uterine contractions has not been supported by more recent evidence, but the advice remains to reserve stimulants rather than lead with them, and to use the minimum effective duration.
Sodium picosulfate and docusate are generally avoided in pregnancy as first options because of limited data.
The quiet intervention: switching iron
Iron supplements are one of the most common drivers of constipation in pregnancy, and the UK pharmacy has an unusually direct lever here. Ferrous sulfate, the cheapest and most commonly prescribed form, is also the most reliably constipating. Ferrous fumarate and ferrous gluconate deliver similar amounts of elemental iron but are frequently better tolerated.
Because all three are routinely available as pharmacy-only formulations, a pharmacist can sometimes propose a swap without a GP appointment — particularly for supplements bought over-the-counter rather than prescribed. Where the iron is prescribed, a short conversation with the GP practice will usually see the formulation changed.
See our iron supplement tolerability guide for how pharmacies compare the options.
What UK pharmacies will not supply
- Castor oil is not recommended in pregnancy at any stage.
- Magnesium sulfate (Epsom salts) orally is generally avoided.
- Liquid paraffin is not recommended in pregnancy because of aspiration and absorption-of-fat-soluble-vitamins concerns.
When to refer rather than treat at the counter
A UK community pharmacy should refer rather than dispense OTC in any of the following scenarios:
- Rectal bleeding beyond minor streaking from a small haemorrhoid
- Unexplained weight loss
- Persistent abdominal pain
- Constipation that appears suddenly with severe discomfort
- Any symptom the pharmacist judges could be obstetric rather than bowel — e.g. reduced fetal movements, localised abdominal pain, pelvic pressure
- Constipation that has not responded to a two-week trial of bulk-former and lactulose at appropriate doses
Summary for the counter
| Step | Option | Onset | Notes |
|---|---|---|---|
| 1 | Fibre, fluids, activity | Days | Often sufficient |
| 2 | Ispaghula husk (Fybogel) | 12–72 h | Take with water |
| 3 | Lactulose or macrogol | 24–48 h | First osmotic choice |
| 4 | Senna, short term | 8–12 h | Reserve; not first line |
| Parallel | Review iron formulation | — | Switch to fumarate/gluconate if sulfate poorly tolerated |
See our broader laxative choice guide for non-pregnancy comparisons.
Sources
- NICE CKS — Constipation, management in pregnancy
- NHS — Constipation in pregnancy
- British National Formulary — Constipation treatment summary
General information for UK pharmacy customers. This does not replace individual medical or midwifery advice; pregnancy-specific questions should always be confirmed with your pharmacist, GP or midwife.