How to Think About Side Effects Versus Disease Symptoms
Why this matters
Attributing symptoms incorrectly leads to poor treatment decisions. Blaming effective medication for symptoms that are actually caused by disease activity risks stopping a treatment unnecessarily. Assuming worsening is disease progression when it’s actually a side effect risks persisting with something that’s causing harm. In both cases, the clinical team needs accurate information to make the right call.
How to distinguish them
Timing is the most useful starting point. Side effects typically emerge within days to weeks of starting a new medication, after dose increases, or when new interacting medications are added. Disease symptoms tend to predate medication, worsen when treatment is reduced or stopped, or follow known flare triggers such as infection or stress. A useful question to ask is: did this symptom appear only after starting or changing medication?
The known side effect profile of the medication also helps. Every medication has predictable side effects. If a symptom isn’t on that list, it’s less likely to be medication-related. For example, methotrexate commonly causes nausea and hair thinning but rarely causes joint pain. Therefore, joint pain in someone taking methotrexate for arthritis is more likely a sign of disease activity than a side effect.
Symptom characteristics provide further clues. New symptom types that have never been experienced before may be side effects. Symptoms that worsen after doses suggest a drug-related cause. Symptoms that improve on drug holidays suggest side effects. Familiar symptom patterns that match previous disease activity are more likely to represent the condition itself.
Objective markers can help resolve ambiguity. Rising inflammatory markers suggest disease activity, not side effects. Abnormal liver function tests suggest medication toxicity, if on a hepatotoxic drug. Normal inflammatory markers alongside worsening symptoms make a medication cause more likely.
Common scenarios that can be confusing
- Fatigue. Both disease and many medications cause it. Tracking whether fatigue correlates with dose timing or with disease activity markers helps distinguish the two
- Nausea. If it peaks a few hours after taking medication and improves with dose changes or anti-nausea measures, it’s likely medication-related
- Rashes. Both immune conditions and medications cause rashes. Timing relative to starting treatment, distribution, and associated features all help differentiate
What you could do
- Don’t stop medication abruptly if side effects are suspected. Contact the GP or specialist first, as many are manageable without stopping treatment
- Document clearly when symptoms started, how they relate to medication doses, their severity, and any patterns
- Report symptoms without concluding the cause. A clinician can assess probability based on pharmacology, disease patterns, and examination far more reliably than self-attribution alone
- Track symptoms and medication together so that timing relationships become visible over time
This article is for general information purposes only and doesn’t constitute legal, financial or benefits advice. For advice specific to your situation, please speak to a qualified professional or contact an organisation such as Citizens Advice, who may be able to assist you further.
References:
‘Diagnosis and management of rheumatoid arthritis: a review’ (2018) https://doi.org/10.1001/jama.2018.13103
‘Joining the DoTS: new approach to classifying adverse drug reactions’ (2003) https://doi.org/10.1136/bmj.327.7425.1222