The most important side effect of treatment with metamizole is the development of agranulocytosis, defined as a drop in neutrophilic granulocytes below < 500µL/µl blood [
5,
9,
11]. It should be noted that metamizole-dependent blood count changes, although rarely, also include pancytopenia [
9]. Incidence and risk of MIA remain unclear and vary widely: depending on the study, it was 1.5 to 40 times more likely to develop agranulocytosis with metamizole than if the drug was not administered [
2,
3]. The IAAAS initially reported an incidence of one case per 1,100,000 user weeks or 6.2 cases per million per year [
4]. Further studies in Germany and Spain seemed to support these results [
5,
13]. The Berlin Case–Control Surveillance Study [
5], a prospective study on adult patients with acute non-chemotherapy-induced agranulocytosis identified by active surveillance in all 51 Berlin hospitals between 2000 and 2010, reported an even lower incidence rate of 0.96 cases per million inhabitants per year, while a retrospective analysis of reports from Switzerland revealed an estimated incidence rate of 0.46–1.63 per million person-days of use [
14]. On the other hand, a Swedish study in 1999 calculated an incidence of one case of agranulocytosis at 1439 prescriptions, resulting to a new removal of metamizole from the Swedish market, after having previously been reinstated following the results of IAAAS [
7,
15]. This study was criticized due to being a retrospective analysis based on only 8 MIA cases, but recent evidence from Germany seems to confirm these findings, with a recent retrospective analysis from the years 2010–2013 published in 2019 examining new diagnosis of agranulocytosis or neutropenia identified through ICD code, reporting a risk of 1:1602 to develop agranulocytosis and neutropenia per patient and metamizole prescription [
15]. However, the calculated risk in this study might be overestimated, as it does not distinguish between neutropenia and agranulocytosis.