Does Restricting Pack Size of Paracetamol (Acetaminophen) Reduce Suicides?

P ublic health interventions are usually implemented without any attempt to prospectively evaluate them with an experimental research design. Thus the only way to evaluate the outcome of the intervention is to describe what happened before and after its implementation. In a new study published in PLoS Medicine, Morgan et al. have examined the change in deaths attributed to paracetamol (acetaminophen) poisoning in England and Wales in the six years before and after a legislated reduction in the maximum pack size [1]. The average number of deaths preceding the regulation was 212/year and afterwards it fell to an average of 154/year (see Figure 1 and Table 1 in [1]). Therefore, readers could be forgiven for being puzzled that the authors have declared that they found little evidence to suggest that the regulations caused the reduction. The authors did show statistically signifi cant changes in deaths attributed to paracetamol poisoning after the legislation compared to the preceding six years before the legislation (Table 2 in [1]). But they also assessed whether the observed changes over time were unique to paracetamol. They compared the changes against the number of poisoning deaths involving compound paracetamol (not covered by the regulations), aspirin, antidepressants, and against the number of non-poisoning suicide deaths, over the same time period. It is the lack of statistically signifi cant and consistent changes in the relative rates of deaths for paracetamol versus coincidental changes for other drugs (Table 4 in [1]) that lead the authors to conclude that the regulations may have had no effect. The changes seen with each of the comparator drugs in this study might each have an explanation that would cast the regulatory effect in a more favourable light. For a start, the regulations also applied to aspirin—so it is hardly surprising that a similar reduction was noted for aspirin fatalities at the same time. Indeed the reductions in death from both paracetamol and from aspirin could be considered as further evidence of the effectiveness of the regulations. Second, it is likely that some deaths attributed to paracetamol compounds are deaths where there has also been substantial co-ingestion of non-compound paracetamol, since people commonly ingest more than one medication in overdose. Deaths in these circumstances due to paracetamol hepatotoxicity may still be classifi ed as due to paracetamol compound, so the reduction in paracetamol compound deaths may, in part, have resulted from the legislation [2]. Conversely, …