Study finds possibly problematic drug combos being prescribed to older adults

If you take multiple medications, you might be unknowingly taking one drug to treat the side effects of another.

In a new study published in the BMJ that looked at the prescription data of older adults in Ontario, Canada, researchers identified 24 common drug combinations that may occur when a drug side effect "is misinterpreted as a new condition, and then a second drug is started to manage the adverse event," said lead author Paula Rochon, director of research at the Weston and O'Born Centre for Mature Women's Health at Sinai Health in Toronto. The researchers call this sort of chain reaction a "potentially inappropriate prescribing cascade."

It can be easier than you'd think for a side effect to masquerade as a new diagnosis. They're not always as obvious as, for instance, a rash that develops the day after starting a medication, Rochon said. "They can happen sometimes weeks to months or even longer after beginning a drug, so people don't always make the connection."

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For example, consider how a doctor might prescribe a nonsteroidal anti-inflammatory medication (NSAID) to manage chronic back pain. With time, the medication can raise blood pressure , which may lead to a prescription of a blood-pressure-lowering drug — rather than a reevaluation of the original treatment plan.

Certain side effects — say, weight gain or constipation — can be easy to blame on lifestyle changes, for instance shifts in sleep, diet or physical activity. Many people also see different doctors for distinct conditions, and medication info isn't always recorded in great detail, making it tricky to pinpoint when new symptoms might be drug side effects. "Older people may be particularly at risk [of inappropriate prescribing] because as you get older, you often develop more chronic conditions and are therefore on more medications," Rochon said.

This study suggests that "if a patient comes in with a new symptom that could be plausibly linked to a medicine after they've started that medicine, we really do need to be thinking, step one, have we caused this?" said Alexander Chaitoff, an assistant professor of internal medicine at the University of Michigan Medical School who researches the safety and efficacy of medications in older adults. (He was not involved in the study.)

In 2025, Rochon worked with an international team of experts in geriatric medicine and pharmacology to come to a consensus on a comprehensive list of potentially inappropriate prescribing cascades, ultimately identifying 65 of them. For the new study, she and her team measured the prevalence of each drug combo in a population of over 2 million older adults to learn which of the cascades they'd identified were the most critical for clinicians to watch out for.

By analyzing how common each initial drug was in this population, how often it was followed by the second drug and how strong the link was between the two, the researchers determined the 24 potentially inappropriate prescribing patterns that were most prevalent. (This research focused on one patient population, so it's possible that other inappropriate drug cascades might be more common in other groups.)

To note, Rochon said that while the final list is a helpful tool for clinicians to spot possibly problematic drug pairings in action, it shouldn't be thought of as a definitive record of drug combos to avoid. Rather, the important lesson for patients and providers alike is that inappropriate prescribing cascades can and do happen, especially in older adults.

(To see other drug pairings that could be an inappropriate prescribing cascade, check out eTable 3 in the study .)

In certain circumstances, it does make sense to treat the side effects of a medication with a second drug. "Sometimes the risks of an additional medication are outweighed by the benefit of continuing the first," Chaitoff explained. However, these drug cascades should prompt a clinician to pause, Rochon said, to first consider if new symptoms leading to a prescription are the effects of a previously prescribed drug, and if so, whether it's worth continuing both medications.

The risk in failing to recognize a symptom as a drug side effect is that it can lead to the wrong kind of treatment. For example, a common type of blood pressure medication called a calcium channel blocker may cause ankle swelling. If a doctor doesn't put two and two together, they might prescribe a diuretic to flush excess fluid, Chaitoff explained. But that won't solve the problem, which is triggered by how the medication changes the pressure inside blood vessels — not water retention. Needlessly taking a diuretic could also raise the risk of dehydration.

Even when a drug successfully resolves a side effect of a different drug, it may not be sensible to stay on both. The more medications you take overall, the greater the chance of experiencing adverse effects, Chaitoff said. You also might end up spending a lot of money on a prescription you could have avoided taking by adjusting the original medication.

It's important to know that all of the common medications analyzed in the study have important, sometimes lifesaving, value. Plenty of people may also be prescribed the first medication in any of the identified drug combos and not have side effects that lead to another prescription, Chaitoff said. And as noted above, taking both medications in a prescribing cascade is sometimes appropriate.

The key takeaway is the importance of carefully tracking every medication you use — the name and dose, when and why it was started and for what reason — in one place, Rochon said. If you have that information, you're more likely to catch a potentially problematic pattern.

While the study didn't account for drugs that patients chose to buy over-the-counter and begin of their own accord, Rochon emphasized the importance of adding these to your list, too. (Several of the drugs in the study are also available over-the-counter.)

Asking questions when a doctor recommends a new medication can also help you avoid a possibly unnecessary or problematic prescription. Rochon suggests first asking if the symptom they're aiming to treat with a new drug is potentially an effect of a drug you're on. If a particular prescription comes into question, you could also ask if there's a safe way to take a break from it and see if you feel better, Chaitoff said.

If a symptom does seem to be a side effect of a drug, it's worth asking whether that drug is truly still necessary for you and if it's possible to consider an alternative option or change the dose, Rochon said.

Ultimately, the right drugs for you will depend on your unique health history, goals and preferences. "Everybody should feel empowered to review their medications and possible side effects with their doctors, and to say, 'Can we try something different?' if they do feel that a symptom they're experiencing is related to a medication," Chaitoff said.