Under-reporting of adverse drug reactions
Background
Voluntary reporting systems for adverse drug reactions (ADRs) were developed in the 1960s following the problem of birth defects caused by thalidomide. Their main purpose is early detection of unexpected potential harmful effects of medicines. It is well-known that not all adverse drug reactions will be reported through such schemes i.e. that there is under-reporting. Over the years many studies have been conducted to estimate the extent of under-reporting in different settings. In this study researchers from the DSRU systematically reviewed the medical literature and brought together all the relevant evidence.
Methods
Standard techniques were used to search the medical literature prior to April 2004. Numerical estimates of under-reporting were extracted from the publications or calculated from the information provided, and expressed as percentages.
Results
In total, 37 relevant studies were identified from 12 different countries. These provided 43 estimates of the degree of under-reporting of ADRs. The overall average was 94% with half of the estimates falling within the range 82-98%. This means that, on average, these studies found that only 6% of ADRs were reported. There was no clear difference between studies based on general practice and those based on hospitals. As was expected, the degree of under-reporting tended to be less for more serious or severe ADRs but, in 19 studies which looked at specific serious/severe ADRs, the average under-reporting rate was still high at 85%.
Conclusions
This study shows that under-reporting of ADRs, including those which are serious or severe, is widespread. Further work is needed to assess the public health implications of under-reporting and the potential impact of initiatives to improve levels of ADR reporting.