Metformin
Cities measured
87
Detected in
87 / 87
Elevated / alert
5
Highest
1.42 μg/L — Delhi
Overview
Metformin is the world's most prescribed anti-diabetic drug, taken daily by over 200 million people. It is excreted largely unchanged and detected in rivers, groundwater, and tap water worldwide at concentrations that track global diabetes prevalence.
Health Relevance
At drinking water concentrations, direct health effects in humans are not established. Metformin's transformation product guanylurea has shown reproductive and metabolic effects on aquatic invertebrates.
Regulatory Limits
Drinking Water Directive 2020/2184
No EU regulatory limit.
Controversy & Contested Science
A 2021 PNAS study found guanylurea (the primary metformin transformation product) at 140–500 ng/L in European river water. A 2022 Canadian study found metformin in drinking water in 9 of 10 tested cities. Metformin's ubiquity reflects both the global diabetes epidemic and its near-complete resistance to conventional wastewater treatment. Some researchers raise concern about a feedback loop: environmental metformin could theoretically affect gluconeogenesis in aquatic organisms and — in chronic low-level dietary exposure — in humans, though this has not been demonstrated.