Anticholinergic burden: what it means and why medicines are reviewed

Acetylcholine is a chemical messenger used in the brain and in the nerves that control muscles, the gut, the bladder and other organs. Anticholinergic medicines block its action. According to the Right Decisions polypharmacy guidance for Scotland, this can be useful: such medicines help regulate muscles in the intestines and bladder and are used in Parkinson's disease and COPD.

The problem is that many medicines have anticholinergic effects as a side effect, even when that is not their main purpose. The guidance gives tricyclic antidepressants and antihistamines as examples. When several are taken together, their effects are cumulative. That combined exposure is called anticholinergic burden.

Because the effect adds up across a medicine list, anticholinergic burden is a medication-safety concept rather than a disease. It is usually discussed in the context of polypharmacy, which means taking many medicines at once.

The Scottish guidance says anticholinergic medicines have long been recognised as causing dry mouth, constipation and urinary retention, and that exposure has more recently been linked to impaired cognition and physical decline. There may also be an association with falls, increased mortality and cardiovascular events. It also lists blurred vision as a peripheral effect.

Effects are dose dependent and sensitivity varies a great deal between individuals, so some people notice problems on one medicine while others tolerate several. The guidance notes that medicines with anticholinergic properties continue to be commonly prescribed to older people and those with mental health conditions, who are particularly susceptible to adverse effects, even at therapeutic doses.

NICE's dementia guideline says to be aware that some commonly prescribed medicines are associated with increased anticholinergic burden and therefore cognitive impairment. It advises that reversible causes of cognitive decline, including cognitive impairment from medicines with increased anticholinergic burden, should be investigated before referral to a specialist dementia diagnostic service if dementia is still suspected.

It also says to consider minimising the use of such medicines, and if possible to look for alternatives, when assessing whether to refer a person with suspected dementia and during medication reviews with people living with dementia. The Scottish guidance says reducing anticholinergic burden may result in improvements in short-term memory, confusion, behaviours and delirium.

Importantly, NICE does not say these medicines cause dementia. The point is that they can impair thinking and may mimic or worsen symptoms, so they are a reversible factor worth checking.

The Scottish guidance includes a table based on the modified anticholinergic risk scale to guide where burden is likely to be highest. It cautions that this is a developing area with disagreements between sources and that some of the table is based on incomplete evidence or expert opinion.

The Scottish guidance says scales such as the anticholinergic cognitive burden scale and the anticholinergic risk scale can be used to assign a cumulative score to a person's medicines. NICE noted that there are validated scales but insufficient evidence to recommend one over the others.

The guidance stresses that the overall aim is to reduce total anticholinergic exposure as much as possible and that a person-centred approach is essential, because individual sensitivity and the benefit of each medicine differ. Some therapeutic areas are highly specialised, such as Parkinson's disease, and need expert advice before any change.

The recommendations in the Scottish guidance include practising caution when prescribing medicines with anticholinergic burden, prescribing only the minimum needed especially for older adults, people with frailty or complex multimorbidity, and carefully considering whether the benefit outweighs the risk. It says a pharmacist-led medication review with feedback to the prescriber can lead to a significant reduction in burden, and that in people with dementia a medication review should minimise medicines that may adversely affect cognitive function and avoid anticholinergics together with acetylcholinesterase inhibitors.

For patients and carers, the practical message is to bring a full list of medicines, including those bought over the counter, to a review, and to ask whether any can be stopped, reduced or replaced. Do not stop a medicine yourself. Some medicines should be reduced gradually, and stopping a treatment for a condition such as Parkinson's disease or depression can cause harm.

On the NHS, medication reviews are carried out by the prescriber or a pharmacist, and the Scottish guidance notes that a pharmacist-led review with feedback to the prescriber can reduce burden. It is reasonable to ask for a review after a fall, a hospital stay or a change in memory.

Private pharmacists and GPs can also carry out medication reviews, but any changes should be shared with the GP who prescribes your repeat medicines so that your records stay accurate.