Constipation

Constipation is the result of stool spending too long in the colon. The longer it stays, the more water gets reabsorbed, and the harder and drier it becomes. The slowing can come from gut movement itself, from pelvic floor problems that make passing the stool hard, or from a mix. Most cases are functional, meaning there is no structural cause.

• Low fibre intake. UK average is about 20 grams a day against a recommended 30 grams.
• Low fluid intake or chronic mild dehydration.
• Sedentary lifestyle. Movement helps gut transit.
• Slowing medications: opioids, some antidepressants, iron supplements, calcium-channel blockers, and GLP-1 receptor agonists like Ozempic, Wegovy and Mounjaro.
• Pregnancy. Around a third of pregnant women experience constipation across pregnancy, peaking in the second trimester.
• Hypothyroidism. Underactive thyroid slows the whole metabolism, including the gut.
• Pelvic floor dysfunction. Muscles do not coordinate properly during defaecation.
• Stress and changes in routine, especially travel.

NICE and NHS guidance suggests trying these in sequence. Each step takes a week or two to work. Avoid jumping straight to laxatives.

1. Hydration: 2 to 2.5 litres a day, every day. Extra fluid mainly helps if you are actually dehydrated; on its own it does not reliably improve constipation, but it pairs well with fibre.
2. Soluble fibre: psyllium husk (Fybogel, Metamucil), taken with plenty of fluid. A pharmacist can advise on amounts. Soluble fibre has clearer evidence for improving symptoms than insoluble fibre, which is less consistent. Do not add bulk at all if you are passing nothing: fibre on a gut that has stopped moving makes things worse.
3. Movement: 20 to 30 minutes of walking a day stimulates the gastrocolic reflex. This single intervention has decent evidence on its own.
4. An osmotic laxative, which holds water in the colon so the stool stays soft. Guidelines put macrogol first (Movicol or Laxido in the UK, polyethylene glycol or Miralax in the US): the joint AGA and ACG guideline gives it a strong recommendation for chronic constipation, and magnesium oxide a conditional one. Magnesium oxide, not citrate, is the form the trials used, which is the opposite of the advice usually found online. On how much: supplemental magnesium is capped at 400 mg a day by UK guidance and 350 mg by the US limit, with diarrhoea as the effect that sets the ceiling. Going above that is using it deliberately as a laxative, and that is a conversation with a pharmacist or your prescriber rather than a number off a page, particularly if your kidneys are anything other than normal.
5. Stimulant laxatives like senna and bisacodyl. Effective but for occasional use. Long-term daily use can lead to colon dependence.

Call 999 in the UK, or 911 in the US, if you have stopped passing stool or wind altogether and have a swollen abdomen and vomiting. That combination can mean an obstruction. See a doctor for any of these alongside the constipation: blood in stool, unintentional weight loss, persistent abdominal pain, no bowel movement for four or more days despite the steps above, or a change in bowel habit that has not settled. On that last one, NICE now recommends a simple stool test (FIT) for an unexplained change in bowel habit at any age with no minimum duration, and separately flags age 40 and over with weight loss and abdominal pain, or 50 and over with rectal bleeding, for urgent checks. A strong family history of bowel cancer also lowers the bar for getting checked. These are the signs to take to a doctor rather than manage alone.

• Detox teas. Most are senna under another name. They are not a wellness intervention.
• Cutting all fibre. Sometimes recommended online. It typically makes the underlying problem worse.
• Coffee enemas. No evidence of benefit. Real risk of harm.
• Sitting on the toilet for ages with the phone. Pelvic floor strain leads to haemorrhoids and worsens incomplete evacuation.