Geriatric pharmacology
How ageing changes the response to medicines, why many medicines at once is risky, and how medicines are reviewed and reduced safely.
Older adults use the most medicines and have the most adverse reactions. Ageing changes body composition and kidney function, the brain becomes more sensitive to many drugs, and several illnesses are often treated at once. Most reactions are preventable by choosing drugs carefully, adjusting for kidney function and reviewing the list regularly.
Pharmacokinetic changes
- Distribution: less body water and lean mass, more fat; albumin can fall with illness or poor nutrition.
- Metabolism: liver blood flow and some phase I reactions decline, with wide variation between people.
- Elimination: kidney filtration falls in many older adults; creatinine alone can hide this because muscle mass is lower.
- Result: many drugs need lower doses or longer intervals, especially those cleared by the kidney.
Greater sensitivity
Older people respond more strongly to benzodiazepines, opioids, anticholinergic drugs and blood pressure medicines. Baroreflexes are slower, so orthostatic hypotension is more frequent, and dizziness from it raises the risk of falls and fractures. Geriatric syndromes such as falls, delirium, frailty and incontinence are often worsened, or caused, by medicines.
Potentially inappropriate medicines
The American Geriatrics Society Beers Criteria (2023 update) list drugs to avoid or use with caution in older adults, drugs that worsen particular diseases, risky combinations and drugs needing kidney adjustment. Examples include strongly anticholinergic drugs (first-generation antihistamines, some antidepressants and antispasmodics), benzodiazepines and Z-drugs, long-term oral NSAIDs, sulfonylureas, sliding-scale insulin, and pethidine.
Polypharmacy and cascades
Many older people take several medicines at once. Each added drug increases the chance of interactions and errors. In a prescribing cascade, a side effect is mistaken for a new disease and treated with another drug, for example metoclopramide causing parkinsonism that is then treated with an antiparkinson drug. WHO's Medication Without Harm challenge names polypharmacy as one of its three priority areas.
Medication review and deprescribing
A structured review checks every medicine against its current indication, benefit, risk and the patient's goals, includes over-the-counter products and supplements, and plans a gradual stop or dose reduction where appropriate. Patients and carers are involved in the decisions, and the review is repeated at transitions of care such as hospital discharge.
Test yourself
Think of the answer, then tap the question to see it.
Why can a normal serum creatinine be misleading in an older patient?
Muscle mass falls with age, so less creatinine is produced; kidney function can be reduced even when creatinine looks normal.
Which two drug groups are on the Beers list because they raise the risk of confusion and falls?
Benzodiazepines (and Z-drugs) and strongly anticholinergic drugs such as first-generation antihistamines.
What is a prescribing cascade?
A side effect is misread as a new condition and treated with another drug, adding more risk.
What does a deprescribing review check for each medicine?
Whether its indication still applies, its benefit and harm for this patient and their goals, and whether it can be stopped or reduced safely.
Example drugs
Connections
Educational content on how drugs work; not a prescribing guide and no substitute for a health professional's advice. No doses are given.
Sources: American Geriatrics Society 2023 updated AGS Beers Criteria® for potentially inappropriate medication use in older adults (Journal of the American Geriatrics Society (author manuscript, PubMed Central), 2023); Medication safety in polypharmacy: technical report (World Health Organization, 2019); Ageing and health (World Health Organization, 2026).
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Representative model, for educational purposes only.