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Background: The climate change causes an increasing number of hot days in Europe. Although evidence for a temperature-depending increase in adverse drug reactions exists, no concrete recommendations for dose adjustments of causative drug groups have been established to date. Likewise, no consistent definition of heat-associated symptoms exists.

Materials and Methods: For identification, the multicentric ADRED trial (Adverse Drug Reactions in Emergency Departments, DRKS-ID: DRKS00008979) served as basis, containing patients with a suspected adverse drug reaction in emergency departments, symptoms and medication including WHO-UMC causality assessments of all drugs taken. The cases were linked with temperature data of Germany’s National Meteorological Service (DWD) at enrolment date and in three-day-mean before enrolment. Symptoms were visually identified using heatmaps, while relative frequency of symptoms in the group with causally accused diuretic (n = 1050) vs. not causally accused diuretic (n = 2330) were compared in dependence of daily maximum and mean temperature. Focus was set on summer days and hot days according to DWD (daily maximum temperature ≥ 25°C). A literature comparison was conducted for plausibility.

Results: The identified symptoms included vertigo (rel. frequency in subgroup with causally accused diuretics ≥ 25°C, n = 182: 17.6%), dehydration (14.3%), syncope (12.1%), electrolyte imbalance (11.5%), hypotonia (10.4%), fall (10.4%), peripheral oedema (7.1%), vomiting (7.1%), fatigue (7.1%). They showed both a higher relative frequency in the group with causally accused diuretics and temperature-dependency, especially at summer/ hot days. The difference between various temperature parameters was negligible. No unanticipated symptoms were observed.

Conclusion: The analysis showed clear association between identified symptoms and higher temperatures in real-world data and will be further used to develop recommendations for temperature-dependent dose adjustments.