A new study has highlighted a hidden problem in medication use: one drug can cause a side effect that is mistaken for a new medical condition, leading to another prescription rather than a review of the original treatment.

Researchers in Ontario identified 24 common prescribing cascades that may expose older adults to avoidable harm and increase healthcare costs.

The findings were published in BMJ and led by Dr. Paula Rochon of Sinai Health in Toronto.

What Is A Prescribing Cascade?

A prescribing cascade develops when a side effect caused by one medication is interpreted as a separate illness and treated with an additional drug.

One example involves non-steroidal anti-inflammatory drugs, or NSAIDs, which are widely used for pain relief. These medicines can increase blood pressure. If that change is treated as a new case of hypertension without considering whether the original medication is responsible, another prescription may be added unnecessarily.

Older adults may be particularly vulnerable because they are more likely to have several health conditions and take multiple medications at the same time.

Rochon explained that these medication chains are common but can easily be overlooked in everyday clinical practice. She stressed that knowing what medicines a patient takes, when each one was started and why it was prescribed is essential for recognising whether a new symptom could actually be related to an existing treatment.

Researchers Found 24 Common Patterns

The project involved an international group of specialists in geriatric medicine, internal medicine and clinical pharmacology. In earlier research, 12 experts developed a list of 65 potentially inappropriate prescribing cascades.

For the latest analysis, that list was compared with population-level prescription information from ICES, Ontario’s health data institute.

Researchers examined how frequently the first medication was prescribed, how often another medicine followed it and how strongly the two prescriptions appeared to be connected.

This process identified 24 prescribing cascades that were both commonly observed and considered capable of causing harm.

Why Older Adults Face Greater Risk

When several medications are taken at once, it becomes harder to determine whether a new symptom represents a separate medical condition or an adverse reaction to an existing drug.

Problems such as dizziness, swelling, increased blood pressure or digestive discomfort can have many possible explanations. Without a careful review of the medication timeline, a side effect may be treated as a completely new illness.

The researchers also highlighted potential concerns for mature women, who may experience more chronic conditions over their lifetimes, receive more drug treatments and have a greater likelihood of adverse medication events.

Communication Could Prevent Unnecessary Prescriptions

According to Rochon, one of the biggest problems is that patients and healthcare professionals may not always discuss how one prescription could be connected to the next.

Looking only at a current medication list may therefore be insufficient. Clinicians may also need to consider when every drug was introduced and whether a newer prescription appeared after a known side effect developed.

This type of review could help distinguish between a genuine new condition and a reaction to a previous treatment.

Technology And Pharmacists May Help

Researchers believe automated clinical systems could help identify suspicious prescription sequences. A digital alert, for example, could warn a clinician when a newly prescribed medicine is commonly used to manage a known side effect of another drug already being taken.

Pharmacists could also have a larger role in reviewing complex medication combinations and identifying patterns that deserve further assessment.

The study does not suggest that every additional prescription is unnecessary. Instead, it shows why medications should be viewed as part of a connected treatment history. Regularly reviewing when and why each drug was started may help reduce avoidable prescribing and improve medication safety, particularly among older adults.