When one medicine leads to another: 24 prescribing cascades to watch in older adults

Twenty four potentially inappropriate prescribing cascades, where a side effect of one drug is treated with another, met all priority criteria in more than two million older adults in Ontario, Canada, in a study published Sept. 10, 2026, in The BMJ. Iron supplements followed by laxatives was the most common, a key point about medicines in older adults.

A prescribing cascade happens when a side effect of one medicine is mistaken for a new problem and treated with a second medicine. Older adults, who often take several drugs, are especially exposed.

What did the study look at?

Researchers used health records of more than two million community-dwelling adults aged 66 or older in Ontario, Canada, of whom 54.3% were women. They started from 65 potentially inappropriate cascades chosen by international experts in 2025. For each, they measured how many people took the first drug, how often the second drug followed, and whether the second drug appeared after the first more often than expected by chance.

What did the study find about medicines in older adults?

• Twenty four cascades (37%) met all three priority criteria.
• Heart and blood pressure medicines were the most frequent starting drugs.
• The most common cascades were iron supplement to laxative (11.9%), statin to pain reliever (10.9%) and cholinesterase inhibitor, a dementia medicine, to sleep medicine (10.3%).
• The strongest sequence was corticosteroid to antipsychotic (adjusted sequence ratio 2.55).
• Results were similar in men and women, except for antidepressants followed by bladder medicines, which was stronger in men.

Why does this matter?

Iron can cause constipation, statins can cause muscle aches, and dementia medicines can disturb sleep or cause nausea. Each new drug adds cost and new risks. A prioritized list helps doctors and pharmacists spot these chains and consider adjusting the first drug instead of adding a second.

How solid is this evidence?

It’s moderate. Mongevity rates it C on our A-to-E scale: a very large population study with a well-established method. Limits: the method shows timing patterns, not proof that each second drug was prescribed for a side effect; some prescriptions may have been appropriate; and data come from one Canadian province.

What are the open questions?

It remains to be tested whether alerts or pharmacist reviews based on this list reduce cascades and improve health, and whether the same cascades top the list in other countries.

What does this mean for you?

If you or an older relative start a new medicine and soon develop a new symptom, ask whether the symptom could be a side effect before adding another drug. Bringing a full medicine list to each visit makes these chains easier to spot. Don’t stop any medicine on your own.

How do I explain this at dinner?

Sometimes a pill causes a side effect, and instead of changing that pill, a doctor adds another one to treat the side effect. Researchers looked at more than two million older Canadians and found 24 of these chains worth watching, like iron pills followed by laxatives. A good question for the table: has anyone here started a medicine to fix what another one caused?

In one sentence: a population study of older adults in Ontario identified 24 high-priority potentially inappropriate prescribing cascades, led by iron supplement to laxative.