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In a recent meta-analysis, Roberts and coworkers have raised several concerns about the safety profile of paracetamol.1 The criticism was supported by a clear association between exposure and risk of major end points (all-cause mortality, cardiovascular disease (CVD), hypertension, gastrointestinal (GI) disorders, renal failure) and a clear demonstration of a dose–response effect. Although Roberts's message is not conclusive—authors themselves suggest the need of further meta-analyses—it surely has a relevant burden in terms of public health being paracetamol the most largely used drug as first-line therapy for pain disorders.
We present a critical revision of Roberts's meta-analysis following a step-by-step analytical approach.
First, the quality of cohort studies included in the meta-analysis is overtly and intrinsically low.
The authors broadly ascribe the low degree of internal validity of studies collected for the meta-analysis using the GRADE method,2 although this tool is likely unsuitable for quality assessment of non-experimental studies.1
Instead, we adopted the Cochrane A Cochrane Risk Of Bias Assessment Tool (ACROBAT) checklist, which is specifically tailored on observational investigations.3 By doing so, we identified several major methodological pitfalls among the collected studies (table 1).
Second, most of the discussed examples fail to demonstrate a convincing dose–response effect.
A clear dose–response effect was only revealed for the increased incidence of hypertension estimated by two severely biased studies based on Nurse's Health Study cohort5 ,9 (see the following paragraphs for the details). Notably, Roberts and coworkers support the presence of a dose–response gradient for studies where this relation was instead represented by a plateau (outcome: mortality6); by a U-shaped curve (outcome: mortality,7 GI haemorrhage7); by an ascending trend followed by a clamorous final reverse (outcome: …
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