Duphalac (Lactulose) vs. Other Laxatives: Detailed Comparison

When treating constipation, Duphalac (Lactulose) is a synthetic disaccharide that pulls water into the colon, softening stool and encouraging regular bowel movements. It’s been on the market for decades and is often the first prescription doctors reach for. But you’re not limited to one option - a range of over‑the‑counter and prescription alternatives exist, each with its own pros, cons, and sweet spots.

Why compare? What you’ll get out of this guide

• Clear picture of how Duphalac works compared with the most common substitutes.
• Side‑effect profiles side‑by‑side, so you know what to expect.
• Practical tips for choosing the right agent based on lifestyle, age, and medical history.
• A handy table you can print or bookmark for quick reference.
• Answers to the most frequent follow‑up questions, all in one place.

How Duphalac (Lactulose) actually works

Lactulose is a non‑absorbable sugar. When you swallow it, it travels unchanged through the stomach and small intestine. In the colon, gut bacteria ferment it into short‑chain fatty acids. This fermentation process creates an osmotic gradient that draws water into the bowel lumen, swelling the stool and stimulating peristalsis. The result? Softer stools and more frequent movements, usually within 24‑48 hours.

Top alternatives at a glance

Below are the five most frequently used substitutes. They fall into three categories: osmotic agents, stimulant laxatives, and bulk‑forming agents.

1. Polyethylene glycol (PEG) - an osmotic powder you dissolve in water.
2. Senna - a plant‑based stimulant that triggers colonic muscles.
3. Bisacodyl - a synthetic stimulant available as tablets or suppositories.
4. Magnesium hydroxide - a mineral salt that works osmoticly, often sold as “Milk of Magnesia”.
5. Dietary fiber (psyllium, wheat bran) - a bulk‑forming agent that adds volume to stool.

Side‑effect snapshot: what to watch for

Every laxative can cause discomfort if taken wrong. Here’s a quick rundown:

• Duphalac: bloating, flatulence, and occasional diarrhea if the dose is too high.
• PEG: rare allergic reactions, mild nausea, and a temporary increase in bowel urgency.
• Senna: cramping, electrolyte imbalance with long‑term use, and possible dependency.
• Bisacodyl: sharp abdominal pain, cramps, and risk of dehydration if overused.
• Magnesium hydroxide: loose stools, hypermagnesemia in patients with kidney failure.
• Dietary fiber: gas, bloating, and if not taken with enough water, it can actually worsen constipation.

Speed vs. sustainability: choosing the right tool

If you need relief fast (e.g., before a travel trip), osmotic agents like Duphalac or PEG usually work within a day. Stimulants such as senna and bisacodyl kick in a bit quicker-often 6‑12 hours-but they can cause stronger cramps. Bulk‑forming fibers are the slow‑and‑steady option; they may take 2‑3 days to show effect but are ideal for long‑term maintenance without the risk of dependence.

Special populations: who should avoid what?

Pregnant women, children, and elderly patients have different tolerances. Duphalac is generally considered safe in pregnancy (category B) and is frequently prescribed to children because it’s not absorbed systemically. PEG, on the other hand, is safe for most adults but lacks robust pediatric data. Senna and bisacodyl should be used cautiously in the elderly due to the risk of severe cramps and dehydration. Magnesium hydroxide is contraindicated for people with renal impairment. Fiber supplements are usually safe for all ages, provided fluid intake is adequate.

Cost and accessibility in the UK (2025 snapshot)

Prices fluctuate, but as of October 2025:

• Duphalac 15 ml syrup (250 ml) - £4.80 (NHS prescription often free).
• PEG 3350 (7 g powder) - £6.20 for a month's supply (over‑the‑counter).
• Senna tablets (10 mg) - £2.50 for a 28‑day pack.
• Bisacodyl tablets (5 mg) - £3.10 for 30 tablets.
• Magnesium hydroxide suspension - £2.90 for 200 ml.
• Psyllium husk (100 g) - £1.80.

Prescription coverage makes Duphalac the most affordable for many patients, while the others rely on self‑pay.

Quick reference table

How to decide which option fits you best

Use the following decision flow:

1. Do you need immediate relief (within a day)?
   Yes → Pick an osmotic agent (Duphalac or PEG) or a stimulant (senna/bisacodyl). No → Consider fiber.
2. Are you pregnant or caring for a child?
   Yes → Duphalac or fiber are safest.
3. Do you have kidney disease?
   Yes → Avoid magnesium hydroxide; stick with Duphalac or PEG.
4. Is cost a major factor?
   Yes → Check NHS prescription eligibility for Duphalac; otherwise fiber is cheapest.

When in doubt, start low and go slow. A half‑dose of Duphalac can often ease mild constipation without the gas that a full dose might cause.

Potential pitfalls and how to avoid them

• Ignoring fluid intake - Osmotic agents need water to work. If you’re not drinking enough, you may get worse bloating.
• Taking multiple laxatives together - This can cause severe diarrhea and electrolyte loss.
• Using stimulants long‑term - The colon can become dependent, making natural bowel movements harder.
• Skipping dietary fibre - Even if you’re on medication, a low‑fiber diet undermines long‑term health.

Real‑world scenarios

Case 1 - A 35‑year‑old office worker with occasional constipation. She tried increasing water and walking more, but symptoms persisted. Starting with a low dose of Duphalac (15 ml nightly) cleared the issue in two days, and she stayed on it once a week for maintenance.

Case 2 - A 68‑year‑old man on multiple meds, including antihypertensives. He developed chronic constipation after adding a calcium supplement. His doctor switched him from Duphalac to a fiber supplement (psyllium) plus a small daily dose of PEG, which balanced his electrolytes and reduced dependence on prescription meds.

Case 3 - A pregnant woman in her second trimester. Her obstetrician recommended Duphalac because it’s safe and effective, avoiding stimulant laxatives that could cause uterine cramping.

Bottom line

Duphalac (Lactulose) remains a solid, low‑risk choice for most people, especially when safety in pregnancy or children matters. Alternatives like PEG are equally effective and often cheaper over the counter, while stimulant laxatives provide rapid relief but carry higher side‑effect risks. Fiber is the cheapest, safest long‑term strategy, but it works slower.

Think about how quickly you need relief, any health conditions you have, and your budget. Then pick the tool that matches those priorities. And remember: the best constipation plan combines medication (if needed) with plenty of water, regular movement, and a fiber‑rich diet.

Frequently Asked Questions

Armed with this comparison, you can talk to your pharmacist or GP with confidence and choose the right constipation solution for you.