Constipation, laxatives and the drugs that cause the problem in the first place

Constipation affects a substantial proportion of community-dwelling older adults and the majority of those in residential care. It is unglamorous, under-discussed and genuinely consequential: it causes abdominal pain, nausea, reduced appetite, urinary retention, delirium, and — at the severe end — faecal impaction with overflow diarrhoea, which is regularly misdiagnosed and treated with the exactly wrong drug.

In people with dementia it is one of the commoner precipitants of sudden agitation, and it should be near the top of the checklist when behaviour changes abruptly.

Why it becomes more common

Transit time slows modestly with age, but the larger contributors are external.

Reduced mobility reduces colonic motility. Reduced food and fluid intake reduces stool volume. Medications are probably the single biggest factor. Ignoring the urge, whether from mobility problems, an inaccessible toilet, or lack of privacy in a care setting, allows more water to be absorbed and the stool to harden. And pelvic floor dysfunction — difficulty coordinating the muscles needed to evacuate — is common and rarely assessed.

The drug list, which is where to start

Before adding a laxative, it is worth checking whether something already prescribed is causing the problem.

• Opioids, including codeine in combination painkillers and tramadol. Tolerance to the constipating effect does not develop, unlike the analgesic effect.
• Anticholinergics — older antihistamines, tricyclics, bladder antimuscarinics, some antipsychotics.
• Calcium channel blockers, especially verapamil.
• Iron and calcium supplements.
• Antacids containing aluminium.
• Diuretics, indirectly.
• Some antiemetics and antiparkinsonian drugs.

The laxative classes, and how to use them

Bulk-forming — ispaghula, psyllium, methylcellulose. They work by increasing stool volume and require adequate fluid. They are a poor choice in people with reduced fluid intake, poor mobility or opioid-induced constipation, where they can worsen impaction. This is a common prescribing error.

Osmotic — macrogol (polyethylene glycol), lactulose. Macrogol has the best evidence in older adults and is generally first-line: it draws water into the bowel, works reliably, and is well tolerated. Lactulose causes more bloating and wind, which patients dislike, and is less effective in head-to-head comparisons.

Stimulant — senna, bisacodyl. They increase peristalsis and are effective. The old belief that long-term use damages the bowel or produces dependence is not well supported by evidence, and fear of it leads to under-treatment of people who genuinely need regular stimulant laxatives — particularly those on opioids.

Softeners — docusate. Widely prescribed and with disappointing evidence; trials have generally found it little better than placebo.

Suppositories and enemas for rectal loading, where the problem is evacuation rather than transit.

Newer agents — prucalopride, linaclotide, lubiprostone — for chronic constipation refractory to standard treatment, and peripherally acting mu-opioid antagonists such as naloxegol specifically for opioid-induced constipation, where they target the mechanism directly without reversing analgesia.

Opioid-induced constipation is a special case

It should be anticipated rather than treated after the fact. Anyone started on a regular opioid should be started on a laxative at the same time — usually a stimulant plus an osmotic. Bulk-forming laxatives are specifically not recommended here.

This is one of the more reliable prescribing improvements available, and it is still frequently omitted.

The non-drug measures, with realistic expectations

Fibre helps where intake is low, and should be increased gradually with adequate fluid. It is much less effective in slow-transit constipation and can worsen symptoms in some people.

Fluid helps where intake is inadequate; drinking more than you need does not produce softer stools.

Physical activity helps modestly and is worth doing for many other reasons.

Toileting posture and routine are the underrated ones. The gastrocolic reflex is strongest in the thirty minutes after a meal, particularly breakfast — so sitting on the toilet after breakfast, unhurried, is a genuine intervention. Raising the feet on a small stool changes the anorectal angle and reduces straining. Both are free, and both work better than most people expect.

Impaction and overflow

Worth recognising because the intuitive response is wrong. A person with faecal impaction may pass liquid stool around the blockage, appearing to have diarrhoea. Treating that with an antidiarrhoeal makes it considerably worse.

Any older adult with new diarrhoea, particularly with abdominal discomfort and a history of constipation, should have the possibility of impaction considered — and it is usually identified with a simple rectal examination that is often not performed.