Open your pill organizer. Now ask one question about every pill in it: What is this for?
If any answer is “for the constipation,” “for the aches” or “for the trouble sleeping,” ask a second question. Did that problem show up after you started a different pill?
That’s a prescribing cascade, and a study of nearly 2.3 million seniors says it’s happening constantly, because nobody’s watching the whole board.
What a prescribing cascade is
Here’s the plain-English version. You take drug A. Drug A causes a side effect. Nobody connects the side effect to drug A, so it gets treated as a brand-new condition — with drug B.
Now you’re taking two pills. The second one exists only because of the first. And drug B has side effects of its own, which can start the whole thing over.
We explained how these chain reactions get started recently; this new study is the first to put hard numbers on which ones are actually happening.
One example from the researchers themselves: An over-the-counter anti-inflammatory like ibuprofen or naproxen can nudge blood pressure upward. A doctor sees the higher reading and writes a prescription for a blood pressure medication. The patient now has a hypertension diagnosis that might just be a pain reliever talking.
The study
The research was published in The BMJ and was led by Dr. Paula Rochon of the Lunenfeld-Tanenbaum Research Institute and the University of Toronto, using Ontario’s province-wide health data at ICES.
The team started with 65 candidate cascades, assembled in 2025 by an international panel of 12 specialists in geriatrics, internal medicine and clinical pharmacology. Then they checked every one of them against real prescription records for nearly 2.3 million Ontario residents 66 and older, using 2022 and 2023 data.
A cascade made the final cut only if it cleared three bars. The first drug had to be common, taken by at least 5% of the population. The second had to follow in at least 1% of those people within a year.
And the order had to matter: A before B far more often than B before A.
Twenty-four of the 65 cleared all three.
“These sequences of events are common but often missed in clinical practice,” Rochon said in a ScienceDaily release on the study.
The chains the study flagged
Below are the standouts. The percentage is how often the second drug followed the first within a year. The ratio measures direction: A 2.5 means A led to B roughly two and a half times as often as the reverse, a strong hint that A is doing the causing.
1. Iron supplements to laxatives. The most common chain of all: 11.9% of people who started iron were on a laxative within a year. Iron is famously constipating. The fix is often a different iron dose or form, not a second pill.
2. Statins to pain relievers. 10.9%. Muscle aches are the classic statin complaint. Whether the statin’s actually to blame is still debated. We previously covered a large study asking whether that symptom is really linked to cholesterol drugs. Either way, the pain pill gets prescribed.
3. Dementia drugs to sleep medications. 10.3%. Cholinesterase inhibitors, the standard Alzheimer’s medications, can disrupt sleep. Sleep aids in older adults raise fall risk. That’s a chain with a hard landing.
4. Steroids to antipsychotics. The strongest directional signal in the study, a ratio of 2.55. Corticosteroids like prednisone can cause agitation and confusion. Treated as a psychiatric problem, that gets an antipsychotic.
5. Laxatives to anti-diarrheals. Ratio 2.53. You read that right: The drug for the constipation caused diarrhea, so a third drug arrived to stop it. If the constipation came from iron, that’s three pills chasing one.
6. Dementia drugs to anti-nausea medication. Ratio 2.24. Same Alzheimer’s drugs, different side effect, another prescription.
7. Antidepressants to overactive bladder drugs. Common SSRIs (selective serotonin reuptake inhibitors) and SNRIs (serotonin and norepinephrine reuptake inhibitors) were linked to new bladder prescriptions, and the signal was stronger in men (ratio 1.21) than women (1.02). Bladder drugs can bring their own confusion and dry mouth.
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Why this keeps happening
Blame the system, not your doctor and not yourself.
Older Americans take a lot of pills. Federal survey data shows 88.6% of adults 65 and older took a prescription medication in 2021 and 2022. An earlier CDC comparison found 34.5% of Americans ages 60 to 79 took five or more in a month.
Five pills from three prescribers who don’t share notes are a lot of moving parts. Add a short appointment and a new complaint, and the quickest route is a new prescription. That’s my read on the mechanics, not a finding of the study.
What the study authors do say is that clinicians should trace any new symptom back through the existing medication list before adding anything. They also call for pharmacists to have a bigger seat at the table and for electronic alerts that flag known cascades.
What to do about it
Don’t stop anything on your own. Some of these drugs are dangerous to quit abruptly, and the study can’t tell you which prescriptions in your organizer are cascades and which are legitimately needed. Only someone who knows your history can.
Do this instead.
Bring every bottle to one appointment. Prescriptions, supplements, over-the-counter painkillers, the works. The Ontario data couldn’t even see over-the-counter drugs, which means the real cascade count is probably higher than 24.
For each pill, know three things: what it’s for, when you started it and who prescribed it. Rochon’s team says exactly that information is what makes a cascade visible.
Then ask one question: “Could this be a side effect of something else I take?” Ask it about every symptom that got its own prescription.
Use the free review Medicare already pays for. The yearly wellness visit costs you nothing if your provider accepts assignment, and Medicare.gov lists reviewing your current prescriptions as part of it. We’ve covered why that visit is worth showing up for.
If you have Part D and multiple chronic conditions, ask your plan about Medication Therapy Management. Plans must offer it to people who qualify, at no cost, and it includes a full medication review with a pharmacist, plus a written summary and a to-do list.
The fine print
This is an observational study of Canadians, inferred from the timing of prescriptions. The researchers couldn’t see why any second drug was written, didn’t measure health outcomes and are careful to say they detected signals, not proof. Some of those second prescriptions were surely appropriate.
So the right word is “linked,” not “caused.” And in the ways that count here, Canada’s system looks a lot like ours: many prescribers, many pills, nobody owning the whole list.
I’ve spent a career telling people to question anything that’s being done to them after 65 without a clear reason. Your pill organizer deserves the same skepticism.
Bottom line? Twenty-four chains, 2.3 million people, and the most common one starts with an iron pill. Go count your bottles. Then ask the question.
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