Constipation: Which Laxative Does What, and Which to Try First

The laxative shelf is genuinely confusing, and people often end up reaching for a stimulant because it is the one they have heard of. That is rarely the right first move. The four families of laxative work in different ways and suit different problems, and picking the right one usually matters more than picking a brand.

What counts as constipation

There is no correct number of times to go. Some people go three times a day, others three times a week, and both can be entirely normal. Constipation is a change from what is normal for you — going less often, straining, hard or lumpy stools, or feeling like you have not fully emptied.

Before any laxative, the boring advice genuinely works for a lot of people: more fibre gradually, more fluid alongside it, more movement, and not ignoring the urge when it arrives. Fibre without extra fluid can make things worse rather than better.

The four types, and what each is for

Bulk-forming (ispaghula husk, methylcellulose, sterculia) add bulk and hold water in the stool, working with your body’s normal rhythm. They take two to three days and need plenty of fluid. Best first choice for ongoing constipation and for anyone whose diet is short on fibre.

Osmotic (macrogol, lactulose) draw water into the bowel to soften stools. Macrogol usually works within one to three days and is the go-to when stools are hard. Lactulose can take a couple of days and often causes wind and bloating.

Stimulant (senna, bisacodyl) speed up the muscle contractions that move stool along, usually working in six to twelve hours. Useful for short-term relief, especially when a bulk-forming laxative has softened things but nothing is shifting — not for regular long-term use.

Stool softeners (docusate, glycerol suppositories) make hard stool easier to pass, and are helpful where straining needs to be avoided — after surgery, or with haemorrhoids or an anal fissure.

Special situations

In pregnancy, dietary measures come first; if a laxative is needed, bulk-forming is usually tried first, then lactulose or macrogol. Speak to us before starting anything.

Constipation caused by opioid painkillers rarely responds to bulk-forming laxatives — an osmotic, often with a stimulant, is the usual approach. If you have just started codeine or morphine, expect it and plan for it.

In children, doses and choices differ from adults, and constipation in a baby under one should always be discussed with a health professional rather than self-treated.

When to get it checked

See a GP rather than treating it yourself if you have:

• Blood in your stool, or black or tarry stools
• Unexplained weight loss
• A persistent change in bowel habit lasting more than three weeks, especially over 50
• Constipation alternating with diarrhoea
• Severe abdominal pain, vomiting, or a swollen abdomen
• Constipation that does not respond to laxatives at all

Frequently asked questions