How Age Affects Medication Side Effects and Tolerability

Why Older Adults React Differently to Medications

As we age, our bodies change in ways that make medications behave differently-sometimes dangerously so. A pill that worked fine at 50 might cause dizziness, confusion, or a fall at 75. This isn’t just about taking more pills; it’s about how the body handles them. Around 35% of hospital visits for people over 65 are linked to medications, and nearly half of those could have been avoided. The problem isn’t always the drug itself-it’s how aging changes the rules of how drugs work in the body.

How Your Body Processes Drugs Changes With Age

Think of your body like a factory that processes chemicals. As you get older, that factory slows down. Your kidneys filter less, your liver breaks down drugs more slowly, and your body composition shifts. Between ages 25 and 80, total body water drops by about 15%, while fat increases. That means water-soluble drugs like lithium or digoxin stick around longer because there’s less fluid to dilute them. Fat-soluble drugs like diazepam build up in fatty tissue and release slowly, leading to prolonged effects-even if you take the same dose you did at 40.

Renal function declines steadily after 40. By 80, your kidneys may be filtering 30-50% slower than they did at 30. That’s why drugs like antibiotics (aminoglycosides) or heart medications (digoxin) can become toxic if doses aren’t lowered. Liver blood flow also drops by 20-40% between 25 and 65. This affects drugs like propranolol and verapamil that rely on liver metabolism. Even albumin, the protein that carries drugs like warfarin through the blood, decreases by 10-15%. That means more of the drug is free and active in your bloodstream-increasing the risk of bleeding.

Brain and Heart Become More Sensitive

It’s not just how your body moves drugs around-it’s how your organs respond to them. Your brain becomes more sensitive. A standard dose of diazepam causes 50% more sedation and memory loss in older adults than in younger people, even when blood levels are identical. That’s why benzodiazepines like lorazepam or zolpidem are linked to 2-3 times more falls and hip fractures in seniors.

Your heart responds differently too. Beta-blockers like propranolol need 50% higher doses in younger adults to slow the heart, but older adults need less-because their hearts are already less responsive. That’s why a dose that works for a 50-year-old can leave an 80-year-old with dangerously low blood pressure or a slow pulse. Antihypertensives cause orthostatic hypotension (a sudden drop in blood pressure when standing) in 28% of people over 80, compared to just 9% of those aged 50-65. That’s a major cause of falls.

Common Medications That Are Riskier After 65

The American Geriatrics Society updates the Beers Criteria every two years to list drugs that are risky for older adults. The 2023 version highlights 56 medications to avoid or use with extreme caution. Among the most dangerous:

• Anticholinergics like diphenhydramine (Benadryl) and oxybutynin: These cause confusion, memory loss, and delirium. One study found people over 75 are 4.2 times more likely to develop delirium from these drugs than younger adults.
• Benzodiazepines like alprazolam and temazepam: Linked to falls, fractures, and cognitive decline. Zolpidem causes 80% more next-day impairment in seniors.
• NSAIDs like ibuprofen and naproxen: Increase risk of stomach bleeding and kidney damage. Older adults are far more likely to suffer internal bleeding from these over-the-counter painkillers.
• Antidepressants like amitriptyline: Cause urinary retention in men with enlarged prostates and can trigger dangerous heart rhythms.
• Warfarin: Requires lower doses. Older adults have 35% more instability in their INR levels, making bleeding risk unpredictable.

These aren’t just theoretical risks. A 2022 survey of over 1,200 seniors found that 68% reported dizziness or falls tied to medications, 54% had memory problems, and 41% had unexplained weight changes. One Reddit user at 78 started amitriptyline for nerve pain-and ended up needing a catheter within three days due to urinary retention.

Polypharmacy: When More Pills Mean More Danger

Forty-eight percent of adults over 65 take five or more prescription drugs every month. That’s called polypharmacy. It’s not just about the number of pills-it’s about interactions. One drug might slow down how another is processed. A blood thinner might make a painkiller more likely to cause bleeding. A heart medication might worsen kidney function, which then makes another drug build up to toxic levels.

Studies show that 42% of older adults take at least one medication flagged as inappropriate by the Beers Criteria. And 15% of them suffer direct harm from it. The problem is often that doctors prescribe for one condition without seeing the whole picture. A patient on warfarin might get a new antibiotic that interferes with its metabolism. Or someone with arthritis gets an NSAID, then a diuretic for blood pressure, then a benzodiazepine for sleep-all without reviewing how they stack up.

What Doctors Should Do-And What You Can Ask For

Expert guidelines now push for deprescribing-actively stopping medications that are no longer helpful or are too risky. Dr. Michael Steinman, lead author of the 2023 Beers Criteria, says: "We need to stop thinking about adding drugs and start thinking about removing them."

Here’s what you can do:

• Bring all your meds-prescription, over-the-counter, vitamins, supplements-to every appointment. Pharmacists call this a "Brown Bag Review." On average, they find 3.2 medication errors per patient.
• Ask: "Is this still necessary?" Especially if you’re taking a drug for a condition you no longer have, or if you’ve changed goals (e.g., from living 10 more years to living comfortably now).
• Request an eGFR test before starting any kidney-cleared drug. Don’t rely on just a creatinine level-it’s not accurate in older adults.
• Ask about alternatives. Is there a non-drug option for sleep? For pain? For anxiety?
• Get a medication review every 3-6 months if you take five or more drugs. Many hospitals now use the STOPP/START criteria to flag problems.

The Bigger Picture: Why This Matters Now

By 2040, nearly 22% of the U.S. population will be over 65. Right now, preventable drug reactions cost the system $30 billion a year. Hospitals are being penalized for readmissions tied to medication errors in seniors. The FDA now encourages including older adults in clinical trials-but 90% of drug studies still exclude people over 75. That means we’re prescribing based on data from people decades younger.

Progress is happening. Pharmacogenomic testing (checking your genes for how you metabolize drugs) has reduced adverse reactions by 35% in seniors on antidepressants. AI tools like MedAware are cutting errors by 42%. But the real change comes from awareness. If you’re over 65 and on multiple medications, you’re not just a patient-you’re a risk factor. And that means you need to be part of the solution.

What to Do Today

If you or a loved one is over 65 and taking more than three medications:

1. Write down every pill, supplement, and OTC drug you take.
2. Check if any are on the 2023 Beers Criteria list.
3. Ask your doctor: "Could any of these be causing my dizziness, confusion, or constipation?"
4. Ask: "What would happen if I stopped this one?"
5. Request a pharmacist consultation. Many insurance plans cover it.

Medications aren’t the enemy. But treating a 75-year-old like a 45-year-old with the same doses? That’s where the danger lies. The goal isn’t to avoid all drugs-it’s to use the right ones, at the right dose, for the right reason. And that starts with asking questions.

Final Thought: It’s Not About Age-It’s About Biology

Age isn’t the problem. The problem is treating everyone the same. A 70-year-old isn’t just an older version of a 40-year-old-they’re a different physiological system. Medications need to be tailored, not just copied from a standard chart. The good news? You have more power than you think. Ask questions. Demand reviews. Push for safer options. Your body is changing. Your meds should change too.