Changes in precipitation had been reported to affect contaminant levels in water, generally increasing with increased precipitation due to factors such as runoff and combined sewer overflow. Compared to the long term average (1981 to 2010), both 2019 and 2020 experienced a decrease in the annual precipitation (Table ). For the samplings months that were studied in both 2019 and 2020 (April, May, July, and August), 2020 showed the lowest amount of precipitation, which may have contributed to the lower concentration of pharmaceuticals detected. However, the authors acknowledge that more factors are responsible for the observed differences in pharmaceutical contamination in rivers and is not limited to population and precipitation and can be a subject for further investigation. compounds such as caffeine, carbamazepine, lidocaine, and iohexol as some of the more concentrated pharmaceuticals in their study of the Rhine, with sulfamethoxazole as the most abundant antimicrobial. The same study also found antihypertensive drugs such as atenolol, metoprolol, and sotalol. Despite being apart by almost a decade, similar trends can be observed in Luxembourgish waters. Later studies of different parts of the Rhine and Meuse rivers reported similar pharmaceuticals , however, in some studies the anti-diabetic drug metformin and its TP guanylurea were found to be the most abundant pharmaceutical in surface water samples. While metformin was also quantified in this study, the median concentration only ranks 44 th over both years among the pharmaceuticals found. Higher levels of the anti-diabetic drug sitagliptin, 5 th most abundant, were detected in Luxembourg. The two drugs differ in their mode of regulating sugar in the body.