Choosing a Laxative for Chronic or Severe Constipation: What the Evidence Suggests

“Chronic” constipation means symptoms that have lasted a long time, usually starting at least six months ago and continuing for the last three months or more.¹ “Severe” constipation has no strict medical definition; it often describes very uncomfortable symptoms or constipation that does not improve despite use of laxatives, sometimes called “refractory” constipation.²

In terms of treatment, osmotic laxatives — such as lactulose (Duphalac), polyethylene glycol (PEG), and magnesium-based products — are recommended options, with other laxatives added if symptoms continue.¹ There is no single “best” laxative for everyone. The right choice may depend on symptom severity, age, response to treatment, other health conditions, and the advice of a healthcare professional.^{2, 3}

What type of laxative is most effective?

Laxatives come in several main types that work in different ways.^{4, 5} Osmotic laxatives (lactulose, PEG, magnesium-based products) draw water into the bowel to soften stools.^{1, 6} Stimulant laxatives such as senna, bisacodyl, and sodium picosulfate may help move stool along.¹ Bulk-forming laxatives like psyllium add fibre.^{1, 5} Newer prescription options may also be available and these include drugs called secretagogues (lubiprostone, linaclotide, plecanatide), the prokinetic prucalopride, and the bile-acid transporter inhibitor elobixibat.^{1, 4}

Which are suitable laxatives for chronic constipation?

Treatment options include osmotic laxatives, such as lactulose (Duphalac) and PEG for adults with chronic constipation.^{1, 4, 7} Lactulose is reported to have a beneficial effect in relieving constipation and is suitable for long-term use.⁴

Lactulose and PEG are both widely used options. A choice between lactulose and PEG often depends on individual factors such as taste, tolerability, and other medical conditions.^{3, 4} The choice should reflect personal preference together with the guidance of a healthcare professional.^{2, 3}

Lactulose (Duphalac) is a syrup-form laxative for constipation.^{4, 8} It is a sugar-based osmotic laxative that works by drawing water into the bowel.^{2, 8}

What are suitable laxatives for severe constipation?

For severe or hard-to-treat constipation, stimulant laxatives, prokinetics, secretagogues, or bile-acid transporter inhibitors may be added when osmotic laxatives may not be enough.^{4, 6}

Stimulant laxatives such as bisacodyl or sodium picosulfate are also suitable options if constipation does not improve.^{4, 6}

In people with difficulty using the muscles needed for defecation, pelvic floor rehabilitation and biofeedback may help.^{1, 4} Surgery is only considered in very selected cases as a last resort.⁴

How do the main types of laxatives compare?

The table below is a simple, at-a-glance guide to how the main types of laxatives differ — how they work, how quickly they act, and whether they are generally suitable for longer-term use. It is not a comparison of how well they work, which varies from person to person.

Type of laxative (examples)	How it works	Typically works within	Suitable for longer-term use?
Bulk-forming (e.g. psyllium)	Adds fibre so stool holds more water and becomes softer and bulkier	A few days	✔ Yes — often tried first and can be used regularly
Osmotic — e.g. lactulose (Duphalac), PEG	Draw water into the bowel to soften stool	Lactulose: about 2–3 days; PEG: about 1–2 days	✔ Yes — recommended for constipation
Stimulant — e.g. senna, bisacodyl	Encourage the bowel muscles to move stool along	Faster — usually within hours	Best for short-term or occasional use
Stool softener — e.g. docusate	Helps water mix into the stool to soften it	Over a few days	Usually short-term or as needed

General guide only. The right choice depends on your situation — a pharmacist or doctor can help you decide. Sources: ^{1, 3, 4, 6, 8}.

When should you speak with a healthcare professional about laxative use?

Speak with a healthcare professional if constipation is severe, does not improve with laxatives, or if any warning signs appear.⁹

Warning signs that may need medical attention include blood in the stool, a sudden change in bowel habits or unexplained weight loss.^{2, 6} A healthcare professional may suggest tests to rule out other conditions and choose treatment based on age, other medicines, and constipation type.^{2, 6} They may also recommend other prescription medicines or options including surgery.^{4, 6} Many people self-treat with over-the counter laxatives, but professional advice may improve results and quality of life.⁴

Conclusion

There is no single “best” laxative for chronic or severe constipation. Options include osmotic laxatives, such as lactulose and PEG, with stimulants, magnesium-based products, secretagogues, prokinetics, and bile-acid transporter inhibitors as further choices when symptoms continue. ⁴ A conversation with a healthcare professional can help match the choice to the individual.

FAQ

“Severe” constipation has no strict medical definition; it often describes very uncomfortable symptoms or constipation that does not improve despite use of laxatives. It has usually started at least six months ago and continued for the last three months or more.^{1, 2}

Lactulose and polyethylene glycol (PEG) are both widely used osmotic laxatives supported by international guidelines for adults with chronic constipation.^{2, 4, 7} The choice depends on the individual and should be discussed with a healthcare professional.^{2, 3}

Studies suggest that dried plums (prunes), kiwifruit, and partially hydrolysed guar gum may help increase the frequency of bowel movements.^{2, 10} These foods have modest evidence and are sometimes suggested before or alongside laxatives.^{2, 10}

Magnesium oxide and other magnesium-based laxatives have shown benefits over placebo in randomised trials.¹ However, they may raise magnesium levels in the blood, especially in older adults and people with kidney problems.¹ Periodic blood checks may be recommended for people taking these laxatives over a long period.²

Speak with a healthcare professional if constipation lasts a long time, does not improve with laxatives, or if there are warning signs such as bleeding, weight loss, or fever.^{2, 6, 9} A professional can recommend tests and a personalised treatment plan.^{2, 9} Self-treatment is common but may delay the diagnosis of other conditions.^{5, 9}

This article was written with the assistance of generative AI technology and reviewed for accuracy.