The study by Shaheen et al¹ rightly pointed out that some patients with asthma deliberately avoid aspirin and are more likely to use paracetamol, hence a "consumer selection bias". However, they failed to mention the "professional's selection bias". Any standard textbooks or prescribing references state that aspirin and other non-steroidal anti-inflammatory drugs (NSAIDs) could potentially worsen asthma.² Health professionals will therefore certainly choose paracetamol for patients with asthma to avoid potential adverse reactions to NSAIDs and litigation problems.³

It is unlikely that this bias could be resolved by a pharmacoepidemiological study. Recent reports in the general press and television about the study could convey the wrong impression to patients with asthma which could direct them to self-select aspirin or ibuprofen. Fatal or near fatal cases associated with aspirin and NSAIDs have been reported.^4 5 Finally, I agree with Shaheen et al that further studies are required.

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